RS232 configuration diagrams of PC connectors for conection of RS232 devices, with and without handshaking. RequesttoSend RTS hardware flow control is used. RTS signals that data is available for transmission. If the input buffer becomes full, the RTS line will be set. RS2. 32 Serial Cable Wiring. Example cables for connection from a PC to various Lantronix products with DB connectors are provided near the end of this FAQBackground When RS2. DTE Data Terminal Equipment and DCE Data Communications Equipment. Everything would use DB2. DTE to a DCE using a straight through cable and everything would be easy. YDS_Series_Shaking_Laboratory_Sieve_Shaker_7353_2.jpg' alt='Handshake Serial Port Communication' title='Handshake Serial Port Communication' />Handshake Serial Port CHowever, as time went by folks wanted to connect two DTEs or two DCEs to each other, and DB9 connectors started being used, so alternative cable wirings were required. There are no hard and fast rules but in general a DTE will have a male DB2. DB9 connector and a DCE will have a female DB2. DB9.   Other connectors may be used but these are the most common. A typical DTE is a serial port on a terminal,  a Com port on a PC or the serial port on an MSS1. A typical DCE is the serial port on a modem or on a UDS 1. UDS1. 00 or UDS1. If youre connecting a DB2. M DTE to a DB2. 5F DCE an MSS1. Because of this DTE connectors are labeled according to the signal on the pin, DCEs are labeled according to the signal that should be coming from the DTE. In other words a DCE and DTE are labeled identically even though the direction of their signals are opposite. The most common DB2. Protective ground. Transmitted data Out TD or TXD3 Received data In RD or RXD4 Request to send Out RTS5 Clear to send In CTS6 Data set ready In DSR7 Signal ground SG8 Carrier detect In CD or DCD2. Data terminal ready Out DTROriginally all 2. RS232 tambm conhecido por EIA RS232C ou V. DTE terminal de dados, de Data Terminal. The purpose of a nullmodem serial cable is to permit two RS232 devices to communicate with each other without modems or other communication devices between them. DB2. 5 were used but today the above pins are usually the only ones used. The most common pinout for DB9 serial connectors is 1 Carrier detect In CD or DCD2 Received data In RD or RXD3 Transmitted data Out TD or TXD4 Data terminal ready Out DTR5 Signal ground SG6 Data set ready In DSR7 Request to send Out RTS8 Clear to send In CTSStraight through cable. So a cable for a connection from a DB2. DTE to a DB2. 5 DCE is wired DTE                   DCEDB2. M DB2. 5F       DB2. M DB2. 5FTXD   2 2  TXDRXD   3lt lt 3  RXDRTS   4 4  RTSCTS   5lt lt 5  CTSDSR   6lt lt 6  DSRSG    7 7  SGDCD   8lt lt 8  DCDDTR   2. DTRTo connect a DB9. M DTE e. g. the Com Port on a PC to a DB2. F DCE e. g. a modem you would wire your cable like this DTE   5. Cable   DCEDB9. M DB9. F       DB2. 5M DB2. FDCD  1lt lt 8  DCDRXD  2lt lt 3  RXDTXD  3 2  TXDDTR  4 2. DTRSG   5 7  SGDSR  6lt lt 6  DSRRTS  7 4  RTSCTS  8lt lt 5  CTSNull Modems. If all anyone ever wanted to do was connect DTEs to DCEs all you would need are the above straight through cables. But what if you want to connect an MSS1. DTE serial port to a PCs DB2. DTE Com port Thats when you need a null modem. The simplest null modem is the 3 wire connection. On a DB2. 5 DB2. DB2. DB2. TXD 2 3 RXDRXD 3 2 TXDSG  7 7 SGConnecting 2 DB9s youd wire up a null modem this way DB9              DB9. RXD 2 3 TXDTXD 3 2 RXDSG  5 5 SGIf youre using XonXoff software flow control or no flow control this is all you need. A full handshake DB2. DB2. 5          DB2. TXD 2 3 RXDRXD 3 2 TXDRTS 4 5 CTSCTS 5 4 RTSDSR 6 2. DTRDCD 8 SG  7 7 SGDTR 2. DSR 8 DCDThis assures that all flow control handshaking signals are passed from one side of the connection to the other. You should be able to buy a null modem adapter or cable wired this way at any well stocked electronics or computer store. The DB9 version of this may be wired like this DB9 5. Cable   DB9. DCD 1 4 DTRDSR 6 RXD 2 3 TXDTXD 3 2 RXDDTR 4 1 DCD 6 DSRSG  5 5 SGRTS 7 8 CTSCTS 8 7 RTSFinally, a full handshake DB9 to DB2. Null Modem is wired like this DB9              DB2. RXD 2 2 TXDTXD 3 3 RXDDTR 4 6 DSR 8 DCDSG  5 7 SGDSR 6 2. DTRDCD 1 RTS 7 5 CTSCTS 8 4 RTSPC to MSS1. DTE DB2. 5 To connect a PCs DB9. M to a DB2. 5M DTE device like the MSS1. Null Modem cable DB 9. Ffemale                    DB 2. FfemaleRXD 2lt lt 2  TXDTXD 3 3  RXDDTR 4 6  DSRGND 5 7  GNDDSR 6lt lt 2. DTRRTS 7 5  CTSCTS 8lt lt 4  RTSIf your PC has a DB2. M connector for its serial port the Null Modem cable to connect an MSS1. DB 2. 5Ffemale                   DB 2. FfemaleTXD 2 3  RXDRXD 3lt lt 2  TXDRTS 4 5  CTSCTS 5lt lt 4  RTSDSR 6lt lt 2. DTRGND 7 7  GNDDTR 2. DSRPC to MSS4 or other DTE DB9 The Lantronix part number for this cable is 5. DB 9. Ffemale                    DB 9. FfemaleRXD 2lt lt 3 TXDTXD 3 2 RXDDTR 4 6 DSRGND 5 5 GNDDSR 6lt lt 4 DTRRTS 7 8 CTSCTS 8lt lt 7 RTSIf your PC has a DB2. M connector for its serial port the Null Modem cable to connect an MSS4 or similar product is wired like this DB 2. Ffemale                   DB 9. FfemaleTXD 2 2 RXDRXD 3lt lt 3 TXDRTS 4 8 CTSCTS 5lt lt 7 RTSDSR 6lt lt 4 DTRGND 7 5 GNDDTR 2. DSRPC to UDS1. 10. DCE DB2. 5 Use a standard straight through serial cable, often sold as a Modem Cable. The Lantronix part number for this cable is 5. DTE                    DCEDB9. M DB9. F       DB2. M DB2. 5FDCD  1lt lt 8  DCDRXD  2lt lt 3  RXDTXD  3 2  TXDDTR  4 2. DTRSG   5 7  SGDSR  6lt lt 6  DSRRTS  7 4  RTSCTS  8lt lt 5  CTS For decades a 9 pin D subminiature connector has been referred to as a DB9. Recently there has been a movement to use the more accurate DE9 designation. For consistency in our documentation, and to avoid confusion, Lantronix will continue to use the term DB9 to describe a 9 pin D subminiature serial port for the forseeable future. RS 2. 32 Wikipedia. This article is about the RS 2. For RS 2. 32 variants, see serial port. A DB 2. 5 connector as described in the RS 2. In telecommunications, RS 2. Recommended Standard 2. It formally defines the signals connecting between a DTE data terminal equipment such as a computer terminal, and a DCE data circuit terminating equipment or data communication equipment, such as a modem. The RS 2. 32 standard had been commonly used in computerserial ports. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA 2. F Interface Between Data Terminal Equipment and Data Circuit Terminating Equipment Employing Serial Binary Data Interchange, issued in 1. An RS 2. 32 serial port was once a standard feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies, and other peripheral devices. However, RS 2. 32, when compared to other serial interfaces such as RS 4. RS 4. 85 and Ethernet, is hampered by low transmission speed, short maximum cable length, large voltage swing, large standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers, USB has displaced RS 2. Many computers no longer come equipped with RS 2. COM port header that allows the user to install a bracket with a DE 9 port and must use either an external USB to RS 2. RS 2. 32 peripherals. Nevertheless, thanks to their simplicity and past ubiquity, RS 2. Scope of the standardeditThe Electronic Industries Association EIA standard RS 2. C3 as of 1. 96. Electrical signal characteristics such as voltage levels, signaling rate, timing, and slew rate of signals, voltage withstand level, short circuit behavior, and maximum load capacitance. Interface mechanical characteristics, pluggable connectors and pin identification. Functions of each circuit in the interface connector. Standard subsets of interface circuits for selected telecom applications. The standard does not define such elements as the character encoding i. ASCII, EBCDIC, or others, the framing of characters start or stop bits, etc., transmission order of bits, or error detection protocols. The character format and transmission bit rate are set by the serial port hardware which may also contain circuits to convert the internal logic levels to RS 2. The standard does not define bit rates for transmission, except that it says it is intended for bit rates lower than 2. HistoryeditRS 2. Electronic Industries Association EIA as a Recommended Standard. The original DTEs were electromechanical teletypewriters, and the original DCEs were usually modems. When electronic terminals smart and dumb began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS 2. The C revision of the standard was issued in 1. Because the standard did not foresee the requirements of devices such as computers, printers, test instruments, POS terminals, and so on, designers implementing an RS 2. The resulting common problems were non standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes, patch boxes, test equipment, books, and other aids for the connection of disparate equipment. A common deviation from the standard was to drive the signals at a reduced voltage. Some manufacturers therefore built transmitters that supplied 5 V and 5 V and labeled them as RS 2. Later personal computers and other devices started to make use of the standard so that they could connect to existing equipment. For many years, an RS 2. DTE. It remained in widespread use into the late 1. In personal computer peripherals, it has largely been supplanted by other interface standards, such as USB. RS 2. 32 is still used to connect older designs of peripherals, industrial equipment such as PLCs, console ports, and special purpose equipment. The standard has been renamed several times during its history as the sponsoring organization changed its name, and has been variously known as EIA RS 2. EIA 2. 32, and, most recently as TIA 2. The standard continued to be revised and updated by the Electronic Industries Association and since 1. Telecommunications Industry Association TIA. Revision C was issued in a document dated August 1. Revision D was issued in 1. The current revision is TIA 2. F Interface Between Data Terminal Equipment and Data Circuit Terminating Equipment Employing Serial Binary Data Interchange, issued in 1. Changes since Revision C have been in timing and details intended to improve harmonization with the CCITT standard V. Related ITU T standards include V. V. 2. 8 signal voltage and timing characteristics. In revision D of EIA 2. D subminiature connector was formally included as part of the standard it was only referenced in the appendix of RS 2. C. The voltage range was extended to 2. F. Revision E of EIA 2. D shell 2. 6 pin Alt A connector, and made other changes to improve compatibility with CCITT standards V. V. 2. 8 and ISO 2. Overview EIA RS 2. May 1. 96. 0 Interface Between Data Terminal Equipment Data2EIA RS 2. A October 1. 96. EIA RS 2. B October 1. EIA RS 2. C August 1. Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange2EIA EIA 2. D 1. 98. 6TIA TIAEIA 2. E 1. 99. 1 Interface Between Data Terminal Equipment and Data Communications Equipment Employing Serial Binary Data InterchangeTIA TIAEIA 2. F 1. 99. 7 1. 0 0. ANSITIA 2. 32 F 1. R2. 00. 2TIA TIA 2. F R2. 01. 2Limitations of the standardeditBecause RS 2. Issues with the RS 2. Ecd 1200 Software here. The large voltage swings and requirement for positive and negative supplies increases power consumption of the interface and complicates power supply design. The voltage swing requirement also limits the upper speed of a compatible interface. Single ended signaling referred to a common signal ground limits the noise immunity and transmission distance. Multi drop connection among more than two devices is not defined. While multi drop work arounds have been devised, they have limitations in speed and compatibility. The standard does not address the possibility of connecting a DTE directly to a DTE, or a DCE to a DCE. Null modem cables can be used to achieve these connections, but these are not defined by the standard, and some such cables use different connections than others. The definitions of the two ends of the link are asymmetric. This makes the assignment of the role of a newly developed device problematic the designer must decide on either a DTE like or DCE like interface and which connector pin assignments to use. The handshaking and control lines of the interface are intended for the setup and takedown of a dial up communication circuit in particular, the use of handshake lines for flow control is not reliably implemented in many devices. No method is specified for sending power to a device. While a small amount of current can be extracted from the DTR and RTS lines, this is only suitable for low power devices such as mice. The 2. 5 pin D sub connector recommended in the standard is large compared to current practice. Role in modern personal computerseditIn the book PC 9.