RS-232 (Serial Port)

Serial Communication via RS232 Port

2007-11-24T22:19:00.000-08:00

Tutorial sobre Padrão RS-232

2007-09-18T21:06:00.000-07:00

(renamed the "EIA232 Standard" in the early 1990's)

Written by Christopher E. Strangio
Copyright © 1993-2006 by CAMI Research Inc., Acton, Massachusetts
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Contents

What is EIA232?
Likely Problems when Using an EIA232 Interface
Pin Assignments
Cable Wiring Examples (New!)
Signal Definitions
Signal Ground and Shield
Primary Communications Channel
Secondary Communications Channel
Modem Status and Control Signals
Transmitter and Receiver Timing Signals
Channel Test Signals
Electrical Standards
Common Signal Ground
Signal Characteristics
Signal Timing
Accepted Simplifications of the Standard

Pin Description Index

References to EIA Publications

Back to CableEye® Home Page

What is EIA232?
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In the early 1960s, a standards committee, today known as the Electronic Industries Association, developed a common interface standard for data communications equipment. At that time, data communications was thought to mean digital data exchange between a centrally located mainframe computer and a remote computer terminal, or possibly between two terminals without a computer involved. These devices were linked by telephone voice lines, and consequently required a modem at each end for signal translation. While simple in concept, the many opportunities for data error that occur when transmitting data through an analog channel require a relatively complex design. It was thought that a standard was needed first to ensure reliable communication, and second to enable the interconnection of equipment produced by different manufacturers, thereby fostering the benefits of mass production and competition. From these ideas, the RS232 standard was born. It specified signal voltages, signal timing, signal function, a protocol for information exchange, and mechanical connectors.

Over the 40+ years since this standard was developed, the Electronic Industries Association published three modifications, the most recent being the EIA232F standard introduced in 1997. Besides changing the name from RS232 to EIA232, some signal lines were renamed and various new ones were defined, including a shield conductor.

Likely Problems when Using an EIA232 Interface
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During this 40-year-long, rapidly evolving period in electronics, manufacturers adopted simplified versions of this interface for applications that were impossible to envision in the 1960s. Today, virtually all contemporary serial interfaces are EIA232-like in their signal voltages, protocols, and connectors, whether or not a modem is involved. Because no single "simplified" standard was agreed upon, however, many slightly different protocols and cables were created that obligingly mate with any EIA232 connector, but are incompatible with each other. Most of the difficulties you will encounter in EIA232 interfacing include at least one of the following:

1 - The absence or misconnection of flow control (handshaking) signals, resulting in buffer overflow or communications lock-up.

2 - Incorrect communications function (DTE versus DCE) for the cable in use, resulting in the reversal of the Transmit and Receive data lines as well as one or more handshaking lines.

3 - Incorrect connector gender or pin configuration, preventing cable connectors from mating properly.

Fortunately, EIA232 driver circuitry is highly tolerant of misconnections, and will usually survive a drive signal being connected to ground, or two drive signals connected to each other. In any case, if the serial interface between two devices is not operating correctly, disconnect the cable joining this equipment until the problem is isolated.

Pin Assignments
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Go to DTE Pinout (looking into the computer's serial connector)
Go to DCE Pinout (looking into the modem's serial connector)

If the full EIA232 standard is implemented as defined, the equipment at the far end of the connection is named the DTE device (Data Terminal Equipment, usually a computer or terminal), has a male DB25 connector, and utilizes 22 of the 25 available pins for signals or ground. Equipment at the near end of the connection (the telephone line interface) is named the DCE device (Data Circuit-terminating Equipment, usually a modem), has a female DB25 connector, and utilizes the same 22 available pins for signals and ground. The cable linking DTE and DCE devices is a parallel straight-through cable with no cross-overs or self-connects in the connector hoods. If all devices exactly followed this standard, all cables would be identical, and there would be no chance that an incorrectly wired cable could be used. This drawing shows the orientation and connector types for DTE and DCE devices:

EIA232 communication function and connector types for a personal computer and modem. DCE devices are sometimes called "Data Communications Equipment" instead of Data Circuit-terminating Equipment.

Here is the full EIA232 signal definition for the DTE device (usually the PC). The most commonly used signals are shown in bold.

[back to Pin Assignments description]

Copyright © 1993-2002 CAMI Research Inc.

This shows the full EIA232 signal definition for the DCE device (usually the modem). The most commonly used signals are shown in bold.

[back to Pin Assignments description]

Copyright © 1993-2003 CAMI Research Inc.

Many of the 22 signal lines in the EIA232 standard pertain to connections where the DCE device is a modem, and then are used only when the software protocol employs them. For any DCE device that is not a modem, or when two DTE devices are directly linked, far fewer signal lines are necessary.

You may have noticed in the pinout drawings that there is a secondary channel which includes a duplicate set of flow-control signals. This secondary channel provides for management of the remote modem, enabling baud rates to be changed on the fly, retransmission to be requested if a parity error is detected, and other control functions. This secondary channel, when used, is typically set to operate at a very low baud rate in comparison with the primary channel to ensure reliability in the control path. In addition, it may operate as either a simplex, half-duplex, or full-duplex channel, depending on the capabilities of the modem.

Transmitter and receiver timing signals (pins 15, 17, and 24) are used only for a synchronous transmission protocol. For the standard asynchronous 8-bit protocol, external timing signals are unnecessary.

IMPORTANT: Signal names that imply a direction, such as Transmit Data and Receive Data, are named from the point of view of the DTE device. If the EIA232 standard were strictly followed, these signals would have the same name for the same pin number on the DCE side as well. Unfortunately, this is not done in practice by most engineers, probably because no one can keep straight which side is DTE and which is DCE. As a result, direction-sensitive signal names are changed at the DCE side to reflect their drive direction at DCE. The following list gives the conventional usage of signal names:

Cable Wiring Examples
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The following wiring diagrams come from actual cables scanned by the CableEye® PC-Based Cable Test System. CableEye's software automatically draws schematics whenever it tests a cable. Click here to learn more about CableEye.

1 - DB9 All-Line Direct Extension
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This shows a 9-pin DTE-to-DCE serial cable that would result if the EIA232 standard were strictly followed. All 9 pins plus shield are directly extended from DB9 Female to DB9 Male. There are no crossovers or self-connects present. Use this cable to connect modems, printers, or any device that uses a DB9 connector to a PC's serial port.
This cable may also serve as an extension cable to increase the distance between a computer and serial device. Caution: do not exceed 25 feet separation between devices without a signal booster!

80K
Left Side: Connect to DTE (computer) Right Side: Connect to DCE (modem or other serial device)

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2 - DB9 Loopback Connector
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A loopback connector usually consists of a connector without a cable and includes internal wiring to reroute signals back to the sender. This DB9 female connector would attach to a DTE device such as a personal computer. When the computer receives data, it will not know whether the signals it receives come from a remote DCE device set to echo characters, or from a loopback connector. Use loopback connectors to confirm proper operation of the computer's serial port. Once confirmed, insert the serial cable you plan to use and attach the loopback to the end of the serial cable to verify the cable.
In this case, Transmit Data joins to Received Data, Request-to-Send joins to Clear-to-Send, and DTE-Ready joins to DCE-Ready and Received Line Signal Detect.

80K
Left Side: Connect to DTE (computer) Right Side: (none)

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3 - DB9 Null Modem Cable
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
The cable shown below is intended for RS232 asynchronous communications (most PC-based systems). If you are using synchronous communications, the null modem will have additional connections for timing signals, and a DB25 connector would be necessary.
NOTE: Not all null modem cables connect handshaking lines the same way. In this cable, Request-to-Send (RTS, pin 7) asserts the Carrier Detect (pin 1) on the same side and the Clear-to-Send (CTS, pin 8) on the other side of the cable.
This device may also be available in the form of an adapter.

80K
Left Side: Connect to 9-pin DTE (computer) Right Side: Connect to 9-pin DTE (computer)

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4 - DB25 to DB9 Adapter
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Signals on the DB25 DTE side are directly mapped to the DB9 assignments for a DTE device. Use this to adapt a 25-pin COM connector on the back of a computer to mate with a 9-pin serial DCE device, such as a 9-pin serial mouse or modem. This adapter may also be in the form of a cable.

80K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 9-pin DCE (modem)

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5 - DB25 to DB9 Adapter (pin 1 connected to shield)
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This adapter has the same wiring as the previous cable (#4) except that pin 1 is wired to the connector shell (shield). Note that the cable's shield is usually a foil blanket surrounding all conductors running the length of the cable and joining the connector shells. Pin 1 of the EIA232 specification, called out as "shield", may be separate from the earth ground usually associated with the connector shells.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 9-pin DCE (modem)

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6 - DB9 to DB25 Adapter
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Signals on the DB9 DTE side are directly mapped to the DB25 assignments for a DTE device. Use this to adapt a 9-pin COM connector on the back of a computer to mate with a 25-pin serial DCE devices, such as a modem. This adapter may also be in the form of a cable.

80K
Left Side: Connect to 9-pin DTE (computer) Right Side: Connect to 25-pin DCE (modem)

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7 - DB25 All-Line Direct Extension
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This shows a 25-pin DTE-to-DCE serial cable that would result if the EIA232 standard were strictly followed. All 25 pins plus shield are directly extended from DB25 Female to DB25 Male. There are no crossovers or self-connects present. Use this cable to connect modems, printers, or any serial device that uses a DB25 connector to a PC's serial port.
This cable may also serve as an extension cable to increase the distance between computer and serial device. Caution: do not exceed 25 feet separation between devices without a signal booster!
Caution: the male end of this cable (right) also fits a PC's parallel printer port. You may use this cable to extend the length of a printer cable, but DO NOT attach a serial device to the computer's parallel port. Doing so may cause damage to both devices.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DCE (modem)

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8 - DB25 Loopback Connector
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A loopback connector usually consists of a connector without a cable and includes internal wiring to reroute signals back to the sender. This DB25 female connector would attach to a DTE device such as a personal computer. When the computer receives data, it will not know whether the signals it receives come from a remote DCE device set to echo characters, or from a loopback connector. Use loopback connectors to confirm proper operation of the computer's serial port. Once confirmed, insert the serial cable you plan to use and attach the loopback to the end of the serial cable the verify the cable.
In this case, Transmit Data joins to Received Data, Request-to-Send joins to Clear-to-Send, and DTE-Ready joins to DCE-Ready and Received Line Signal Detect.

80K
Left Side: Connect to 25-pin DTE (computer) Right Side: (none)

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9 - DB25 Null Modem (no handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
Note that Pins 11 and 12 are not necessary for this null modem cable to work. As is often the case, the manufacturer of equipment that uses this cable had a proprietary application in mind. We show it here to emphasize that custom serial cables may include connections for which no purpose is clear.
IMPORTANT: This cable employs NO handshaking lines between devices. The handshake signals on each side are artificially made to appear asserted by the use of self-connects on each side of the cable (for example, between pins 4 and 5). Without hardware handshaking, you risk buffer overflow at one or both ends of the transmission unless STX and ETX commands are inserted in the dataflow by software.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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10 - DB25 Null Modem (standard handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
The cable shown below is intended for EIA232 asynchronous communications (most PC-based systems). If you are using synchronous communications, the null modem will have additional connections for timing signals not shown here.
NOTE: Not all null modem cables connect handshaking lines the same way. Refer to the manual for your equipment if you experience problems. In this cable, the DTE Ready (pin 20) on one side asserts the DCE Ready (pin 6) and the Request to Send (pin 5) on the other side.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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11 - DB25 Null Modem (unusual handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
NOTE: Not all null modem cables connect handshaking lines the same way. Refer to the manual for your equipment if you experience problems. In this cable, the DTE Ready (pin 20) on one side asserts the Clear to Send (pin 5), DCE Ready (pin 6), and Carrier Detect (pin 8) on the other side.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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12 - DB25 Null Modem (unusual handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
NOTE: Not all null modem cables connect handshaking lines the same way. Refer to the manual for your equipment if you experience problems. In this cable, the Request-to-Send (pin 4) on one side asserts the Clear-to-Send (pin 5) on the SAME side (self-connect) and the Carrier Detect (pin 8) on the other side. The other handshaking signals are employed in a conventional manner.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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13 - DB25 Null Modem (unusual handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
NOTE: Not all null modem cables connect handshaking lines the same way. Refer to the manual for your equipment if you experience problems. In this cable, the DTE Ready (pin 20) on one side asserts the Clear-to-Send (pin 5) and the DCE Ready (pin 6) on the other side. Request-to-Send (pin 4) on one side asserts Received Line Signal Detect (pin 8) on the other side.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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14 - DB25 Null Modem (unusual handshaking)
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Use this female-to-female cable in any application where you wish to connect two DTE devices (for example, two computers). A male-to-male equivalent of this cable would be used to connect two DCE devices.
NOTE: Not all null modem cables connect handshaking lines the same way. Refer to the manual for your equipment if you experience problems. In this cable, the DTE Ready (pin 20) on one side asserts the DCE Ready (pin 6), and Carrier Detect (pin 8) on the other side. Request to Send (pin 4) is unused, and Clear-to-Send (pin 5) is driven by a proprietary signal (pin 11) determined by the designer of this cable.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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15 - DB25 Null Modem Cable (synchronous communications)
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This female-to-female cable is intended for synchronous EIA232 connections, and is designed to connect two DTE devices. It contains the standard connections of an asynchronous null modem cable, plus additional connections on pins 15, 17, and 24 for synchronous timing signals. To connect two DCE devices, use a male-to-male equivalent of this cable.
For synchronous communications, the null modem cable includes an additional conductor for timing signals, and joins pins 15, 17, and 24 on one side to pins 15 and 17 on the other. Pin 24 on the right side should connect to the timing signal source.

84K
Left Side: Connect to 25-pin DTE (computer) Right Side: Connect to 25-pin DTE (computer)

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16 - DB25 Null Modem Cable (unconventional, may pose risk)
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This simplified null modem cable uses only Request-to-Send (pin 4) and Clear-to-Send (pin 5) as handshaking lines; DTE Ready, DCE Ready, and Carrier Detect are not employed, so this cable should not be used with modems.
CAUTION! Normally, null modem cables have the same gender on each connector (either both male for two DTE devices, or both female for two DCE devices). This cable would be used when the gender on one of the devices does not conform to the standard. However, the opposite genders imply usage as a straight through cable, and if used in that manner will not function. Further, if used as a standard null-modem between two computers, the opposite gender allows you to connect one end to the parallel port, an impermissible situation that may cause hardware damage.

80K
Left Side: Connect to 25-pin DTE (computer) with Gender Changer Right Side: Connect to 25-pin DTE (computer)

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Signal Definitions
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Signal functions in the EIA232 standard can be subdivided into six categories. These categories are summarized below, after which each signal described.

1 - Signal ground and shield.

2 - Primary communications channel. This is used for data interchange, and includes flow control signals.

3 - Secondary communications channel. When implemented, this is used for control of the remote modem, requests for retransmission when errors occur, and governance over the setup of the primary channel.

4 - Modem status and control signals. These signals indicate modem status and provide intermediate checkpoints as the telephone voice channel is established.

5 - Transmitter and receiver timing signals. If a synchronous protocol is used, these signals provide timing information for the transmitter and receiver, which may operate at different baud rates.

6 - Channel test signals. Before data is exchanged, the channel may be tested for its integrity, and the baud rate automatically adjusted to the maximum rate that the channel can support.

Signal Ground and Shield
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Pin 7, Pin 1, and the shell are included in this category. Cables provide separate paths for each, but internal wiring often connects pin 1 and the cable shell/shield to signal ground on pin 7.

Pin 7 - Ground All signals are referenced to a common ground, as defined by the voltage on pin 7. This conductor may or may not be connected to protective ground inside the DCE device. The existence of a defined ground potential within the cable makes the EIA232 standard different from a balanced differential voltage standard, such as EIA530, which provides far greater noise immunity.

Primary Communications Channel
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Pin 2 - Transmitted Data (TxD) This signal is active when data is transmitted from the DTE device to the DCE device. When no data is transmitted, the signal is held in the mark condition (logic '1', negative voltage).

NOTE: Pin 2 on the DCE device is commonly labeled "Received Data", although by the EIA232 standard it should still be called Transmitted Data because the data is thought to be destined for a remote DTE device.

Pin 3 - Received Data (RxD) This signal is active when the DTE device receives data from the DCE device. When no data is transmitted, the signal is held in the mark condition (logic '1', negative voltage).

NOTE: Pin 3 on the DCE device is commonly labeled "Transmitted Data", although by the EIA232 standard it should still be called Received Data because the data is thought to arrive from a remote DTE device.

Pin 4 - Request to Send (RTS) This signal is asserted (logic '0', positive voltage) to prepare the DCE device for accepting transmitted data from the DTE device. Such preparation might include enabling the receive circuits, or setting up the channel direction in half-duplex applications. When the DCE is ready, it acknowledges by asserting Clear to Send.

NOTE: Pin 4 on the DCE device is commonly labeled "Clear to Send", although by the EIA232 standard it should still be called Request to Send because the request is thought to be destined for a remote DTE device.

Pin 5 - Clear to Send (CTS) This signal is asserted (logic '0', positive voltage) by the DCE device to inform the DTE device that transmission may begin. RTS and CTS are commonly used as handshaking signals to moderate the flow of data into the DCE device.

NOTE: Pin 5 on the DCE device is commonly labeled "Request to Send", although by the EIA232 standard it should still be called Clear to Send because the signal is thought to originate from a remote DTE device.

Secondary Communications Channel
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Pin 14 - Secondary Transmitted Data (STxD)

Pin 16 - Secondary Received Data (SRxD)

Pin 19 - Secondary Request to Send (SRTS)

Pin 13 - Secondary Clear to Send (SCTS)

These signals are equivalent to the corresponding signals in the primary communications channel. The baud rate, however, is typically much slower in the secondary channel for increased reliability.

Modem Status and Control Signals
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Pin 6 - DCE Ready (DSR) When originating from a modem, this signal is asserted (logic '0', positive voltage) when the following three conditions are all satisfied:

1 - The modem is connected to an active telephone line that is "off-hook";

2 - The modem is in data mode, not voice or dialing mode; and

3 - The modem has completed dialing or call setup functions and is generating an answer tone.

If the line goes "off-hook", a fault condition is detected, or a voice connection is established, the DCE Ready signal is deasserted (logic '1', negative voltage).

IMPORTANT: If DCE Ready originates from a device other than a modem, it may be asserted to indicate that the device is turned on and ready to function, or it may not be used at all. If unused, DCE Ready should be permanently asserted (logic '0', positive voltage) within the DCE device or by use of a self-connect jumper in the cable. Alternatively, the DTE device may be programmed to ignore this signal.

Pin 20 - DTE Ready (DTR) This signal is asserted (logic '0', positive voltage) by the DTE device when it wishes to open a communications channel. If the DCE device is a modem, the assertion of DTE Ready prepares the modem to be connected to the telephone circuit, and, once connected, maintains the connection. When DTE Ready is deasserted (logic '1', negative voltage), the modem is switched to "on-hook" to terminate the connection.

IMPORTANT: If the DCE device is not a modem, it may require DTE Ready to be asserted before the device can be used, or it may ignore DTE Ready altogether. If the DCE device (for example, a printer) is not responding, confirm that DTE Ready is asserted before you search for other explanations.

Pin 8 - Received Line Signal Detector (CD) (also called carrier detect) This signal is relevant when the DCE device is a modem. It is asserted (logic '0', positive voltage) by the modem when the telephone line is "off-hook", a connection has been established, and an answer tone is being received from the remote modem. The signal is deasserted when no answer tone is being received, or when the answer tone is of inadequate quality to meet the local modem's requirements (perhaps due to a noisy channel).

Pin 12 - Secondary Received Line Signal Detector (SCD) This signal is equivalent to the Received Line Signal Detector (pin 8), but refers to the secondary channel.

Pin 22 - Ring Indicator (RI) This signal is relevant when the DCE device is a modem, and is asserted (logic '0', positive voltage) when a ringing signal is being received from the telephone line. The assertion time of this signal will approximately equal the duration of the ring signal, and it will be deasserted between rings or when no ringing is present.

Pin 23 - Data Signal Rate Selector This signal may originate either in the DTE or DCE devices (but not both), and is used to select one of two prearranged baud rates. The asserted condition (logic '0', positive voltage) selects the higher baud rate.

Transmitter and Receiver Timing Signals
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Pin 15 - Transmitter Signal Element Timing (TC) (also called Transmitter Clock) This signal is relevant only when the DCE device is a modem and is operating with a synchronous protocol. The modem generates this clock signal to control exactly the rate at which data is sent on Transmitted Data (pin 2) from the DTE device to the DCE device. The logic '1' to logic '0' (negative voltage to positive voltage) transition on this line causes a corresponding transition to the next data element on the Transmitted Data line. The modem generates this signal continuously, except when it is performing internal diagnostic functions.

Pin 17 - Receiver Signal Element Timing (RC) (also called Receiver Clock) This signal is similar to TC described above, except that it provides timing information for the DTE receiver.

Pin 24 - Transmitter Signal Element Timing (ETC) (also called External Transmitter Clock) Timing signals are provided by the DTE device for use by a modem. This signal is used only when TC and RC (pins 15 and 17) are not in use. The logic '1' to logic '0' transition (negative voltage to positive voltage) indicates the time-center of the data element. Timing signals will be provided whenever the DTE is turned on, regardless of other signal conditions.

Channel Test Signals
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Pin 18 - Local Loopback (LL) This signal is generated by the DTE device and is used to place the modem into a test state. When Local Loopback is asserted (logic '0', positive voltage), the modem redirects its modulated output signal, which is normally fed into the telephone line, back into its receive circuitry. This enables data generated by the DTE to be echoed back through the local modem to check the condition of the modem circuitry. The modem asserts its Test Mode signal on Pin 25 to acknowledge that it has been placed in local loopback condition.

Pin 21 - Remote Loopback (RL) This signal is generated by the DTE device and is used to place the remote modem into a test state. When Remote Loopback is asserted (logic '0', positive voltage), the remote modem redirects its received data back to its transmitted data input, thereby remodulating the received data and returning it to its source. When the DTE initiates such a test, transmitted data is passed through the local modem, the telephone line, the remote modem, and back, to exercise the channel and confirm its integrity. The remote modem signals the local modem to assert Test Mode on pin 25 when the remote loopback test is underway.

Pin 25 - Test Mode (TM) This signal is relevant only when the DCE device is a modem. When asserted (logic '0', positive voltage), it indicates that the modem is in a Local Loopback or Remote Loopback condition. Other internal self-test conditions may also cause Test Mode to be asserted, and depend on the modem and the network to which it is attached.

Electrical Standards
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The EIA232 standard uses negative, bipolar logic in which a negative voltage signal represents logic '1', and positive voltage represents logic '0'. This probably originated with the pre-RS232 current loop standard used in 1950s-vintage teletype machines in which a flowing current (and hence a low voltage) represents logic '1'. Be aware that the negative logic assignment of EIA232 is the reverse of that found in most modern digital circuit designs. See the inside rear cover of the CableEye manual for a comparison.

Common Signal Ground
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The EIA232 standard includes a common ground reference on Pin 7, and is frequently joined to Pin 1 and a circular shield that surrounds all 25 cable conductors. Data, timing, and control signal voltages are measured with respect to this common ground. EIA232 cannot be used in applications where the equipment on opposite ends of the connection must be electrically isolated.

NOTE: optical isolators may be used to achieve ground isolation, however, this option is not mentioned or included in the EIA232 specification.

Signal Characteristics
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Equivalent Circuit - All signal lines, regardless of whether they provide data, timing, or control information, may be represented by the electrical equivalent circuit shown here:

This is the equivalent circuit for an EIA232 signal line and applies to signals originating at either the DTE or DCE side of the connection. "Co" is not specified in the standard, but is assumed to be small and to consist of parasitic elements only. "Ro" and "Vo" are chosen so that the short-circuit current does not exceed 500ma. The cable length is not specified in the standard; acceptable operation is experienced with cables that are less than 25 feet in length.

Signal State Voltage Assignments - Voltages of -3v to -25v with respect to signal ground (pin 7) are considered logic '1' (the marking condition), whereas voltages of +3v to +25v are considered logic '0' (the spacing condition). The range of voltages between -3v and +3v is considered a transition region for which a signal state is not assigned.

Logic states are assigned to the voltage ranges shown here. Note that this is a "negative logic" convention, which is the reverse of that used in most modern digital designs.

Most contemporary applications will show an open-circuit signal voltage of -8 to -14 volts for logic '1' (mark), and +8 to +14 volts for logic '0' (space). Voltage magnitudes will be slightly less when the generator and receiver are connected (when the DTE and DCE devices are connected with a cable).

IMPORTANT: If you insert an LED signal tester in an EIA232 circuit to view signal states, the signal voltage may drop in magnitude to very near the minimum values of -3v for logic '1', and +3v for logic '0'. Also note that some inexpensive EIA232 peripherals are powered directly from the signal lines to avoid using a power supply of their own. Although this usually works without problems, keep the cable short, and be aware that noise immunity will be reduced.

Short-Circuit Tolerance - The generator is designed to withstand an open-circuit (unconnected) condition, or short-circuit condition between its signal conductor and any other signal conductor, including ground, without sustaining damage to itself or causing damage to any associated circuitry. The receiver is also designed to accept any signal voltage within the range of ±25 volts without sustaining damage.

CAUTION: Inductive loads or magnetically induced voltages resulting from long cables may cause the received voltage to exceed the ±25-volt range momentarily during turn-on transients or other abnormal conditions, possibly causing damage to the generator, receiver, or both. Keep the cable length as short as possible, and avoid running the cable near high-current switching loads like electric motors or relays.

Fail-Safe Signals - Four signals are intended to be fail-safe in that during power-off or cable-disconnected conditions, they default to logic '1' (negative voltage). They are:

Request to Send - Default condition is deasserted.

Sec. Request to Send - Default condition is deasserted.

DTE Ready - Default condition is DTE not ready.

DCE Ready - Default condition is DCE not ready.
Note specifically that if the cable is connected but the power is off in the generator side, or if the cable is disconnected, there should be adequate bias voltage in the receiver to keep the signal above +3v (logic '0') to ensure that the fail-safe requirement is met.

Schmitt triggers or other hysteresis devices may be used to enhance noise immunity in some designs, but should never be adjusted to compromise the fail-safe requirement.

Signal Timing
Next Topic Previous Topic TOC

The EIA232 standard is applicable to data rates of up to 20,000 bits per second (the usual upper limit is 19,200 baud). Fixed baud rates are not set by the EIA232 standard. However, the commonly used values are 300, 1200, 2400, 9600, and 19,200 baud. Other accepted values that are not often used are 110 (mechanical teletype machines), 600, and 4800 baud.

Changes in signal state from logic '1' to logic '0' or vice versa must abide by several requirements, as follows:

1 - Signals that enter the transition region during a change of state must move through the transition region to the opposite signal state without reversing direction or reentering.

2 - For control signals, the transit time through the transition region should be less than 1ms.

3 - For Data and Timing signals, the transit time through the transition region should be
a - less than 1ms for bit periods greater than 25ms,

b - 4% of the bit period for bit periods between 25ms and 125µs,

c - less than 5µs for bit periods less than 125µs.
The rise and fall times of data and timing signals ideally should be equal, but in any case vary by no more than a factor of three.
An acceptable pulse (top) moves through the transition region quickly and without hesitation or reversal. Defective pulses (bottom) could cause data errors.
4 - The slope of the rising and falling edges of a transition should not exceed 30v/µS. Rates higher than this may induce crosstalk in adjacent conductors of a cable.

Note that neither the ASCII alphabet nor the asynchronous serial protocol that defines the start bit, number of data bits, parity bit, and stop bit, is part of the EIA232 specification. For your reference, it is discussed in the Data Communications Basics section of this web site.

Accepted Simplifications of the Standard
Previous Topic TOC

The EIA232 document published by the Electronic Industries Association describes 14 permissible configurations of the original 22-signal standard. Each configuration uses a subset of the 22 defined signals, and serves a more limited communications requirement than that suggested by using all the available 22-signals. Applications for transmit-only, receive-only, half-duplex operation, and similar variations, are described. Unfortunately, connection to DCE devices other than modems is not considered. Because many current serial interface applications involve direct device-to-device connections, manufacturers do not have a standard reference when producing printers, plotters, print spoolers, or other common peripherals. Consequently, you must acquire the service manual for each peripheral device purchased to determine exactly which signals are utilized in its serial interface.

Cable Eyes - Vídeos

2007-09-18T21:02:00.000-07:00

Fonte: Camiresearch

1 Measuring a Cable (3:41, 2.3 MB)
2 Learning a Model Cable (2:44, 2.1 MB)
3 Comparing Two Cables (2:08, 2.3 MB)
4 Testing for Intermittent Connections (5:19, 3.3 MB)
5 Saving Cable Data (3:54, 1.9 MB)
6 Searching the Database (4:27, 3.0 MB)
7 Printing Schematics and Labels (3:46, 3.1 MB)
8 Automatic Testing (4:36, 4.9 MB)
9 Data Logging (6:22,4.5 MB)
10 Wirelist Editing and Cable Design (5:53, 3.0 MB)
11 Adapting to Unusual Connectors (2:43, 10.7 MB)
12 Linking the Software to Custom Interfaces (6:59, 10.4 MB)
13 Testing Wire Harnesses (5:16, 8.6 MB)
14 USB vs. Serial Speed Demo (4:32, 4.2 MB)

For more detailed information on any topic, please refer to the complete CableEye User's Guide available on the CAMI web site in .pdf format.

Fabricantes

2007-09-18T20:27:00.000-07:00

Atac
http://www.atac.com.tw/front/bin/home.phtml

USB 2.0 Video Adapter

Bar Code Pen Scanner

RS-232/422/485 to Fiber Optic Converter

RS232 DB9M 1 Port ExpressCard/34

Parallel/USB Printer to Bluetooth Adapter

Pan/Tilt IP-Camera with IR LED

Wireless Pan/Tilt MPEG-4 IP-Camera

802.11b/g PCI Card

USB 2.0 Extension Cable (5m)

USB to RS-232 Adapter

USB to Parallel Printer Cable

USB 2.0 to SATA/IDE Converter Kit

Serial to Ethernet Converter

Mid-Range CCD Barcode Scanner

Bluetooth v2.0 Mini EDR USB 2.0 Dongle

Links

2007-09-18T20:14:00.000-07:00

Fonte: Google

VGA to Component Cables

vga to 3 rca component cable 3ft to 50ft, lifetime warranty
http://www.cablewholesale.com/

USB to RS-232 Adapter

Connect serial RS-232 device to PC via USB port
http://www.atac.com.tw/

390390-b21 Onsale $44.00

HP-Serial Adapter Port- DB9-M New with Warranty & Free Shipping
http://www.tape4backup.com/

RS232 Sniffer

Recording of line states and data Hard-based micro second time stamps
http://www.iftools.com/

Serial-ATA II cable S-ATA

straight and right angle SATA cable SATA II and power combo cable
http://www.rapidconn.com/

Serial Adapter

Find Serial Adapter Here. Visit our Serial Adapter Guide.
http://all-serialadapter.info/

Actisense USG-1

Isolated USB to serial converter Connects to NMEA 0183 or RS232
www.actisense.com/

USB to TTL Serial Cable

Simple way to connect to USB, Elegant moulded cable. Buy now...
http://www.avitresearch.co.uk/

Bluetooth Serial Adaptor

Replace your RS232 serial cable with wireless Bluetooth adaptor
http://www.free2move.net/

Lock Pins and Pin Kits

Large selection of lock pin kits for all sorts of locks.
http://www.lockpicks.com/

518 Conectores

2007-09-18T19:54:00.000-07:00

	? pin Unspecified
	2 pin MONO plug
	2 pin RCA plug
	3 pin IDC male
	3 pin mini-DIN female
	3 pin mini-din male
	3 pin Panasonic GD 55 cell phone special
	3 pin stereo plug
	3 pin XLR female
	3 pin XLR male
	4 pin 3.5mm (2.5mm) plug
	4 pin Creative SB internal
	4 pin DIN 270° female
	4 pin Garmin round special
	4 pin Garmin special
	4 pin HP video power
	4 pin HP48 calculator special
	4 pin Lowrance special
	4 pin Magellan special
	4 pin mini-DIN female
	4 pin mini-DIN male
	4 pin Mini-Molex power
	4 pin MOLEX 39-01-2040
	4 pin MOLEX 39-29-9042
	4 pin Molex power
	4 pin Nokia 1255 cell phone special
	4 pin Nokia 8270 cell phone special
	4 pin Nokia cell phone special
	4 pin Nokia external cell phone special
	4 pin Philips 530 cell phone special
	4 pin Rino special
	4 pin RJ11 female
	4 pin RJ11 male
	4 pin Siemens SL 10 cell phone special
	4 pin USB A / USB B / mini-USB jack
	4 pin USB A or USB B plug
	4 pin XLR female
	4 pin XLR male
	4 pin, 6 pin or 9 pin IEEE1394 (FireWire) plug
	5 pin Alcatel 311 cell phone special
	5 pin Alcatel BG cell phone special
	5 pin cell phone special
	5 pin conrad special
	5 pin DIN female
	5 pin DIN male
	5 pin I-mobile cell phone special
	5 pin IDC male
	5 pin mini-din
	5 pin mini-USB jack
	5 pin mini-USB plug
	5 pin Nokia 2100 cell phone special
	5 pin Nokia 3650 cell phone special
	5 pin Nokia 5140 cell phone special
	5 pin Nokia 6060 cell phone special
	5 pin Nokia 6100 cell phone special
	5 pin Nokia 6255 cell phone special
	5 pin SQUARE female
	5 pin XLR female
	5 pin XLR male
	6 pin 2x MOLEX 90331-0001
	6 pin 4 pole 1/8 inch plug + 2 rings iPod special
	6 pin ATX AUX power
	6 pin DIN female
	6 pin DIN male
	6 pin Garmin special
	6 pin Kyocera cell phone special plug
	6 pin Lowrance (round) special
	6 pin Lowrance one-row special
	6 pin Lowrance round special
	6 pin mini-DIN female (PS/2 STYLE)
	6 pin mini-DIN male (PS/2 STYLE)
	6 pin MMJ female
	6 pin MMJ male
	6 pin MOLEX 39-01-2060
	6 pin MOLEX 39-30-1060
	6 pin Motorola T192 cell phone special
	6 pin Nokia 2-rows cell phone internal special
	6 pin Nokia 3210 cell phone special
	6 pin Nokia 3510 cell phone special
	6 pin Nokia 6111 cell phone special
	6 pin Nokia 6600 cell phone special
	6 pin Nokia 7610 cell phone special
	6 pin RJ12 (6P6C) female
	6 pin RJ12 (6P6C) male
	6 pin Samsung cell phone special
	6 pin SENDO cell phone special
	6 pin Sendo M550 cell phone special
	6 pin Simcard special
	6 pin XLR female
	6 pin XLR male
	6 pin ZTE cell phone special
	7 pin (16 pads, 7 shown) Nokia E70 cell phone special
	7 pin Alcatel E256 cell phone special
	7 pin female EDGE
	7 pin Garmin special
	7 pin mini-DIN female (key in the center)
	7 pin mini-DIN female
	7 pin MM-card special
	7 pin Nokia 7370 cell phone special
	7 pin Nokia 7390 cell phone special
	7 pin Nokia 8800 cell phone special
	7 pin Nokia E50 cell phone special
	7 pin Nokia E61 cell phone special
	7 pin Nokia N70 cell phone special
	7 pin Nokia N73 cell phone special
	7 pin Panasonic cell phone special
	7 pin Serial ATA motheboard internal
	7 pin SNES special female
	8 pin 4 pole plug + 4 pin iPod special
	8 pin Alcatel cell phone special
	8 pin Chinese cell phone special
	8 pin DIN female
	8 pin DIN male
	8 pin I-mobile cell phone special
	8 pin mini-DIN female
	8 pin mini-DIN male
	8 pin MOLEX 39-01-2080
	8 pin MOLEX 39-29-9082
	8 pin Motorola cell phone special 2 rows
	8 pin Motorola cell phone special
	8 pin Motorola F3 cell phone special
	8 pin Nokia 6260 cell phone special
	8 pin Nokia 8260 cell phone special
	8 pin Nokia 8810 cell phone special
	8 pin RJ45 (8P8C) female
	8 pin RJ45 (8P8C) male
	8 pin SMARTCARD special
	8 pin TURBOVISION TV female
	9 pin Apple mini din
	9 pin D-SUB female
	9 pin D-SUB male
	9 pin mini-din female
	9 pin mini-DIN female special
	9 pin mini-DIN male special
	9 pin Motorola cell phone special
	9 pin Nokia 5110 cell phone special
	9 pin Nokia 6650 cell phone special
	9 pin Nokia 6820 cell phone special
	9 pin Nokia 7210 cell phone special
	9 pin Nokia 7600 cell phone special
	9 pin Nokia 7650 cell phone special
	9 pin Nokia 9500 cell phone special
	9 pin SD-card special
	9 pin Sony Playstation special
	10 pin Alcatel E801 cell phone special
	10 pin Benq cell phone special
	10 pin cell phone special
	10 pin Creative SB 1394 special
	10 pin DIN female
	10 pin I-mobile 503 cell phone special
	10 pin I-mobile cell phone special
	10 pin IDC male
	10 pin Memory stick special
	10 pin mini-din female
	10 pin mini-DIN female special
	10 pin Motorola 6200 cell phone special
	10 pin Motorola d520 cell phone special
	10 pin NEC N343i / Samsung D500 headset cell phone special
	10 pin Nokia 6800 cell phone special
	10 pin Nokia 7280 cell phone special
	10 pin PALM special
	10 pin RJ50 (10P10C) male
	10 pin Samsung handsfree cell phone special
	10 pin ZTE cell phone special
	11 pin Alcatel BH4 cell phone special
	11 pin Ericsson cell phone special
	11 pin Nokia 9210 cell phone special
	11 pin Samsung cell phone special
	12 pin (2 rows) Chinese cell phone special
	12 pin 2x MOLEX 15-48-0106
	12 pin Alcatel cell phone special
	12 pin cell phone special
	12 pin Ericsson cell phone special
	12 pin IDC male
	12 pin iPAQ male special
	12 pin LG handsfree cell phone special
	12 pin Nokia 3250 cell phone special
	12 pin Nokia 5100 cell phone special
	12 pin Nokia 6620 cell phone special
	12 pin Nokia 8110 cell phone special
	12 pin Nokia 8310 cell phone special
	12 pin Nokia 8910 cell phone special
	12 pin Nokia cell phone special
	12 pin plain cell phone special
	12 pin Siemens Lumberg cell phone special
	12 pin Siemens Slim Lumberg cell phone special
	12 pin SNES A/V female special
	12 pin SNES A/V male special
	12 pin SNES EDGE special
	12 pin Sony Playstation special
	12 pin SonyEricsson K750i cell phone special
	12 pin XBox power supply v1.0, v1.1 special
	13 pin 13W3 female
	13 pin Garmin special
	13 pin Mitsubishi cell phone special
	13 pin Mitsubishi Cosmo cell phone special
	13 pin Nokia 5300 cell phone special
	14 pin (2 rows) Chinese cell phone special
	14 pin Apple AAUI female
	14 pin Apple AAUI male
	14 pin Apple PowerBook video
	14 pin Apple video
	14 pin CENTRONICS female
	14 pin Dancal cell phone special
	14 pin DIN male
	14 pin Ericsson cell phone special
	14 pin HP Jornada special
	14 pin Lobster cell phone special
	14 pin Motorola cell phone special
	14 pin Nokia 5500 cell phone special
	14 pin Nokia 9300 cell phone special
	14 pin Nokia pop-port cell phone special
	14 pin Panasonic cell phone special
	14 pin Panasonic X70 cell phone special
	14 pin Philips cell phone special
	14 pin Ricoshet SE
	14 pin Siemens C30 cell phone special
	14 pin Siemens S40 cell phone special
	14 pin SONY BETAMAX female
	14 pin SONY BETAMAX male
	14 pin Sony CMD cell phone special
	14 pin unspecified cell phone special
	15 pin Amiga 3000d power
	15 pin Cisco DB
	15 pin D-SUB female
	15 pin D-SUB male
	15 pin highdensity D-SUB female
	15 pin highdensity D-SUB male
	15 pin Motorola cell phone special
	15 pin Palm special
	15 pin SATA power
	16 pin Bosch 509 cell phone special
	16 pin car OBD2 special
	16 pin cell phone 2 rows w/antenna left special
	16 pin cell phone 2 rows w/antenna right special
	16 pin cell phone special
	16 pin Creative MIDI internal
	16 pin Dell dimension PSU connector
	16 pin NEC cell phone special
	16 pin PALM special
	16 pin PalmOne Treo 650 special
	16 pin Psion II special
	16 pin Qualcomm cell phone special
	16 pin Sharp GX10 cell phone special
	17 pin Motorola V60 cell phone special
	17 pin Nokia 6630 cell phone special
	17 pin Nokia E65 cell phone special
	17 pin Nokia N80 special
	18 pin cell phone 2 rows special
	18 pin LG B1200 cell phone special
	18 pin LG plain cell phone special
	18 pin MOLEX 39-29-9182
	18 pin NEC N610 cell phone special
	18 pin Philips 659 cell phone special
	18 pin Phillips cell phone special
	18 pin Sagem cell phone special
	18 pin Samsung cell phone special
	18 pin Samsung right-to-left numbering cell phone special
	18 pin Samsung SGH-600 cell phone special
	18 pin Sony cell phone special
	18 pin unspecified cell phone special
	18 pin Vitelcom cell phone special
	19 pin (Cannon 19 pin male?)
	19 pin D-SUB female
	19 pin D-SUB male
	19 pin HDMI type A
	19 pin Philips 630 cell phone special
	19 pin Samsung PDA special
	20 pin Apple HDI-20
	20 pin Bosh cell phone special
	20 pin car OBD2 special
	20 pin IDC female
	20 pin IDC male
	20 pin MDR20 female
	20 pin MOLEX 39-01-2200
	20 pin MOLEX 39-29-9202
	20 pin Philips A/V special
	20 pin Samsung cell phone special
	20 pin Samsung E910 cell phone special
	20 pin XBox power supply v1.2, v1.3 special
	21 pin SCART female
	21 pin SCART male
	22 pin Audiovox cell phone special
	22 pin male Himalaya special
	22 pin Maxon cell phone special
	22 pin MOLEX 39-01-2220
	22 pin MOLEX 39-29-9222
	22 pin smartmedia special
	22 pin unspecified special
	23 pin D-SUB female
	23 pin D-SUB male
	23 pin Samsung S100 cell phone special
	24 pin Amiga 3000T power
	24 pin Amphenol male
	24 pin cell phone unspecified special
	24 pin CENTRONICS female
	24 pin DVI-D female
	24 pin DZM 12 DREH
	24 pin LG 7050 cell phone special
	24 pin LG 7050 cell phone special right-to-left numbering
	24 pin MOLEX 39-01-2240 or equivalent
	24 pin MOLEX 44206-0007
	24 pin Pantech cell phone special
	24 pin Samsung cell phone special
	24 pin Samsung E530 cell phone special
	24 pin SUN aux power
	25 pin Cisco DB
	25 pin D-SUB female
	25 pin D-SUB male
	26 pin Asus MyPal special
	26 pin D-SUB
	26 pin hi-density D-SUB
	26 pin IDC male
	26 pin LG cell phone special
	26 pin Sun AUI
	26 pin Toshiba special
	29 pin ATI special
	29 pin DVI female
	30 pin Apple HDI-30
	30 pin iPOD special
	30 pin MOLEX "MicroCross" female
	30 pin MOLEX "MicroCross" male
	30 pin SIMM
	34 pin IDC female
	34 pin IDC male
	34 pin M/34 female
	34 pin M/34 male
	34 pin male EDGE
	34 pin V.35 Cisco
	35 pin Apple ADC "MicroCross" female
	35 pin Apple ADC "MicroCross" male
	35 pin EDGE
	35 pin MOLEX "MicroCross" female
	35 pin MOLEX "MicroCross" male
	36 pin CENTRONICS female
	36 pin CENTRONICS male
	36 pin D-SUB? female
	36 pin Dell Axim special
	36 pin MDR36 female
	36 pin MDR36 male
	36 pin MDR36 SGI female
	37 pin Cisco DB
	37 pin D-SUB female
	37 pin D-SUB male
	40 pin Dell Axim special
	40 pin hi-density D-SUB female
	40 pin hi-density D-SUB male
	40 pin IDC female
	40 pin IDC male
	40 pin Toshiba special
	44 pin IDC (0.75") female
	44 pin IDC (0.75") male
	45 pin Apple HDI-45
	7x47 pin (IEC917 and IEC1076-4-101)
	48 pin Apple ATA
	50 pin Amphenol female
	50 pin Amphenol male
	50 pin CompacFlash female
	50 pin D-SUB female
	50 pin D-SUB male
	50 pin Half Pitch Centronics female
	50 pin Half Pitch Centronics male
	50 pin hi-density D-SUB female
	50 pin hi-density D-SUB male
	50 pin IDC female
	50 pin IDC male
	50 pin M/50 female
	50 pin M/50 male
	56 pin JAMMA special
	58 pin EDGE female
	58 pin EDGE male
	60 pin BURNDY (C-60)
	60 pin Cisco DB
	60 pin CNR bus
	60 pin LFH-60 male
	68 pin female
	68 pin hi-density D-SUB female
	68 pin hi-density D-SUB male
	68 pin male
	72 pin 2x36 EDGE female
	72 pin SIMM
	72 pin SO DIMM
	80 pin SCSI SCA-2 female
	90 pin (36+54) EDGE
	96 pin DIN 41612 (3x32) female
	96 pin Euro-DIN
	96 pin male or female (Fujitsu FCN 234P096-G/Y)
	98 pin (62+36)ISA EDGE female
	98 pin (62+36)ISA EDGE male
	100 pin Mini-PCI Type I/II (Amp 353183-8)
	116 pin MCA bus
	120 pin Euro-DIN
	124 pin (98+22) PCI 5 volt EDGE
	124 pin Mini-PCI Type III (Amp 1318228-1)
	132 pin EDGE (AGP bus)
	144 pin SO SIMM
	146 pin PC/104 16 bit
	152 pin Apple Powerbook PDS
	160 pin DIN 41612 (5x32) female
	168 pin DIMM
	172 pin MCA bus
	184 pin DIMM
	198 pin (62+36/62+38) EISA EDGE
	240 pin DIMM DDR2

WikiBooks sobre Programação Serial

2007-09-18T19:43:00.000-07:00

Fonte: Wikibooks

Serial Programming

Serial Programming:8250 UART Programming

Serial Programming:Complete Wikibook

Serial Programming:DOS Programming

Serial Programming:Error Correction Methods

Serial Programming:Forming Data Packets

Serial Programming:IP Over Serial Connections

Serial Programming:Introduction and OSI Model

Serial Programming:List of Authors

Serial Programming:MAX232 Driver Receiver

Serial Programming:MIL-STD-188 Technical Manual

Serial Programming:Modems and AT Commands

Serial Programming:Modems and AT Commands/& Commands

Serial Programming:Modems and AT Commands/Commands A - M

Serial Programming:Modems and AT Commands/Commands N - Z

Serial Programming:Modems and AT Commands/Result Codes

Serial Programming:Modems and AT Commands/S-Registers

Serial Programming:Modems and AT Commands/Special Commands and Character Sequences

Serial Programming:RS-232 Connections

Serial Programming:RS-232 Technical Manual

Serial Programming:RS-422 Technical Manual

Serial Programming:RS-423 Technical Manual

Serial Programming:RS-449 Technical Manual

Serial Programming:RS-485 Technical Manual

Serial Programming:Serial ATA

Serial Programming:Serial ATA Technical Manual

Serial Programming:Serial Java

Serial Programming:Serial Linux

Serial Programming:Typical RS232-Hardware Configuration

Serial Programming:USB Technical Manual

Serial Programming:Unix

Serial Programming:Win TAPI Programming

Conectores

2007-09-18T18:40:00.000-07:00

Fonte: Wikipedia RS-232, Wikipedia (D-Subminiature)

Os equipamento com intercafe RS-232 podem ser classificados como DTE (Data Terminal Equipment) ou DCE (Data Circuit termination Equipment). Estas definições são necessárias para se estabelecer o equipamento que envia os sinais e o que receberá. O padrão RS-232 recomenda mas não obriga a utilização do connector DB-25 (D-subminiature).

De um modo geral, os equipamentos terminais devem utilizar conectores macho e com as funções definidas na pinagem DTE. Os modems externos utilizam conectores fêmea com as funções definidas nos pinagem DCE. Outros dispositivos podem ter qualquer combinação desses conectores e outras definições para os pinos.

A presença de conector de 25 pinos D-sub não indica necessariamente que uma interface RS-232C está disponível. Por exemplo, no PC IBM original, um conector D-sub Macho era usada para uma porta RS-232C DTE (com uma interface current loop não padronizada em pinos não reservados), mas o conector D-sub fêmea era usado para uma porta de impressora paralela Centronics. Alguns personal computers colocam tensões não padronizadas ou outros tipos de sinais em suas portas seriais.

Conector de 9 Pinos Fêmea

O padrão RS-232 especifica 20 sinais elétricos distintos, sendo que muito dispositivos que utilizam esse padrão fazem uso de apenas alguns desses sinais. Essa utilização seletiva é o que torna possível utilizar conectores menores.

Por exemplo, o conector de 9 pinos DE-9 foi utilizado por muitos PC compatíveis com os IBM PC AT, tendo sido padronizado pela norma TIA-574. Apenas recentemente, mconectores modulares passaram a ser utilizados, tais como, o 8 pinos RJ-45. O padráo EIA/TIA 561 especifica a pinagem para o "Yost Serial Device Wiring Standard" inventado por Dave Yost é muito comum nos computadores Unix mas não nos dispositivos da Cisco Systems.

Muitos equipamentos e dispositivos eletrônicos não utilizam esse padrão. Os conectores de 10 pinos RJ-50 poderáo ser encontrados em alguns dispositivos.

A Digital Equipment Corporation, por exemplo, definiu seu próprio padrão de conexão de sistemas chamado DECconnect que foi baseado nos conectores Modified Modular Jack.

Conector DE-9

O conectis DE-9 (9 pin D-shell connector) é um tipo de conector elétrico D-subminiature mais comumente utilizado para RS 232 (serial port) nos microcomputadore do tipo IBM AT e compatíveis. O DB-9 é um misnomer para o DE-9.

Na verdade um conector DB-9 possui apenas 9 pinos da RS-232 no conector que também estão presentes no conector DB-25, os outros 16 pinos são ausentes.)

a b

Figura 1 - Conector DB-9: (a) macho e (b) fêmea.

Sinais de Entrada RS-232 no Conector DB9

2007-09-18T16:01:00.000-07:00

Fonte: Wikipedia

DCD (Pino 1 - PC Input)

Data Carrier Detect. The on condition of this signal line, as sent by the DCE, informs the DTE that it is receiving a carrier signal from the remote DCE that meets its criteria.

This is a signal to indicate from the communications equipment (DCE) that the phone line is still "connected" and receiving a carrier signal from the modem at the other end. Presumably well-written software or serial equipment could detect from this logic state when the telephone has been "hung up" on the other end. Null-modems often tie DCD to DSR at each end since there is no carrier signal involved. This signal pin can be independently detected by software, and a "real" hacker could have some fun playing with this pin to add some sort of signal to increase bandwidth. Still, it isn't worth the effort, when there are much better ways to increase data throughput....

RxD (Pino 2 - PC Input)

Receive Data line. Serial data from DCE to DTE. When DCD is in the off condition, the RD signal must be in the MARK state.

TxD (Pino 3 - PC Output)

Transmit Data Line. Serial data from DTE to DCE.

The reverse of RX, this is where the terminal equipment (DTE) is transmitting serial data, using the same format and protocol that the receiver is expecting...usually. More on the exact protocol further below. Like RX, think along the lines of "Terminal Transmit" when designing equipment that will be using this pin.

DTR (Pino 4 - PC Output)

Data Terminal Ready. This signal, in conjunction with DSR, indicates equipment readiness.

Basically a signal from the DTE that says "Hello!, I'm ready if you are". This is a general indicator to the DCE that the terminal is ready to start sending and receiving data. If there is some initialization that needs to happen in the communications equipment, this is a way for the terminal equipment to "boot" the receiving equipment.

GND (Pino 5 - Ref. Zero Volts)

Ground. This is an interesting pin to look at. What it does is try to make a common "ground" reference between the equipment that is being connected to compare the voltages for the other signals. Normally this is a good thing, because sometimes different pieces of equipment have different power supplies and are some distance away. The not so pleasant thing about this wire is that it usually is a physical piece of copper that can conduct electricity that is not normally supposed to go down the wire, like a short-circuit or worse yet a bolt of lightning (it happens far more often that you would normally think for this sort of equipment). That can fry both the DCE as well as the DTE. Things like fiber converters and ground isolators can help prevent this from happening, but can still be something to worry about. Over short distances this is generally not a problem.

DSR (Pino 6 - PC Input)

Data Set Ready. A signal turned on by the DCE to indicate to the DTE that it is connected to the line.

This is the counterpart to DTR with the communications equipment (or computer peripheral on the serial line). When the DTR is sent as a signal, the communications equipment should change this signal to -15V to indicate that it is ready to communicate as well. If the DCE goes through a "boot" sequence when the DTR gets signaled, it should not signal DSR until it is complete. But many connectors "hard wire" this pin to be directly connected to the DTR pin at each end to reduce the number of wires needed in the cable. This can be useful for connecting devices using existing telephone wires, but prevents applications from using the DTR and DSR for handshaking.

RTS (Pino 7 - PC Output)

Request To Send. Indicates the DTE is ready to transmit data, and then the DCE must prepare to receive data. After some delays, the DCE turns on the CTS line to inform the DTE it is ready to receive data. Once communication is complete, the DTE turns off the RTS signal. After a brief delay to ensure that all transmitted data has been received, the DCE turns off CTS.

The signal (logical "1"), it indicates to the DCE that the terminal is ready to receive more data. When it has a +15V (logical "0") signal, it indicates that the DCE should stop sending data temporarily until the buffer can be cleared.

CTS (Pino 8 - PC Input)

Clear To Send. Turned on by the DCE to inform the DTE that it is ready to receive data.

This is the response signal from the DCE regarding if the terminal equipment should be transmitting any data. When this signal is -15V the terminal is "permitted" to transmit data. Like the DTR/DSR pins, this one can be directly connected to the RTS pin to reduce the number of wires needed, but this eliminates the possibility of hardware flow control. Some software ignores this pin and the RTS pin, so other flow control systems are also used. That will be explained when we get to actual software.

RI (Pino 9 - PC Input)

Ring Indicator. Turned on by the DCE while ringing is being received.

Again, thinking back to a telephone modem, this is a signal that indicates that the telephone is "ringing". Generally, even on a real telephone modem, this is only occasionally set to -15V for the signal. Basically, when you would normally be hearing a "ring" on your telephone, this pin would be signaled. On Null-modems, often this wire isn't even connected to anything. If you really are connected to a real modem, this does have some strong uses, although there are other ways to have the terminal equipment (like a PC connected to an external modem) be informed that there are ways to communicate this information through the data pins as well. This will be covered lightly in the software section.

Low-Voltage, Single-Supply 232-Standard Interface Solutions (Rev. A)

2007-09-17T20:59:00.000-07:00

Fonte: Texas

Features and key specifications for Texas Instruments (TI) new low-voltage, single-supply, 232-standard-compliant interface devices are presented, as well as test data comparing TI versus competitor same-function devices. Evolution of the 232 standard is discussed relative to TI devices that have significantly greater capability than the 232 standard requires.

Download .pdf (slla083a.pdf, 101 Kbytes)

Interface Circuits for TIA/EIA-232-F (Rev. A)

2007-09-17T20:58:00.000-07:00

Fonte: Texas

This design note provides information concerning the designing of TIA/EIA-232-F interface circuits. The TIA/EIA-232-F standard is covered including the electrical specification, maximum cable lengths, and the DB9S connector. The section entitled Optimizing PC Interface Devices discusses the following topics: SN75C185 power considerations, interface power-consumption calculations, the SN75LP185A and SN75LPE185 devices, on-chip slew rate limiting, and internal noise filtering.

Download .pdf (slla037a.pdf, 127 Kbytes)