RS232 serial cables pinout.RS232 serial cable layoutAlmost nothing in computer interfacing is more confusing than selecting theright RS232 serial cable. These pages are intended to provide informationabout the most common serial RS232 cables in normal computer use, or in more commonlanguage 'How do I connect devices and computers using RS232?' RS232 serial connector pin assignmentThe RS232 connector was originally developed to use 25 pins. In this DB25 connectorpinout provisions were made for a secondary serial RS232 communication channel.In practice, only one serial communication channel with accompanying handshakingis present. Only very few computers have been manufactured where bothserial RS232 channels are implemented.
Examples of this are the Sun SparcStation10 and 20 models and the Dec Alpha Multia.Also on a number of Telebit modem models the secondary channel is present. It can be usedto query the modem status while the modem is on-line and busy communicating.On personal computers, the smaller DB9 version is more commonly usedtoday. The diagrams show the signals common to both connector types inblack. The defined pins only present on the larger connector are shown in red.Note, that the protective ground is assigned to a pin at the large connectorwhere the connector outside is used for that purpose with the DB9 connector version. The pinout is also shown for the DEC modified modular jack.This type of connector has been used on systems built byDigital Equipment Corporation; in the early days one of theleaders in the mainframe world.
Point me to a source that will sell DEC MMJ-DB25 cables wired for rs-422 operation. Here is the pinout for that plug so that you can use a modem/serial Wire#. Send (wht/org) W 10 -ve power (wht/grey) X 22 Ring (blk/org) Y 9 +ve power. You will see that one of the major differences between RS232 and RS422/RS485 is the signaling mode. RS232 is unbalanced while RS422/RS485 is balanced. An unbalanced signal is represented by a single signal wire where a voltage level on that one wire is used to transmit/receive binary 1 and 0: the can be considered a push signal driver.
Althoughthis serial interface is differential (the receive and transmit have their ownfloating ground level which is not the case with regular RS232)it is possible to connect RS232 compatible devices withthis interface because the voltage levels of the bit streams are in the same range.Where the definition of RS232 focussed on the connection of DTE,data terminal equipment (computers, printers, etc.) with DCE,data communication equipment (modems), MMJ was primarily defined for theconnection of two DTE's directly. RS232 DB25 pinout RS232 DB25 to DB9 converterThe original pinout for RS232 was developed for a 25 pins sub D connector.Since the introduction of the smaller serial port on the IBM-AT,9 pins RS232 connectors are commonly used. In mixed applications,a 9 to 25 pins converter can be used to connect connectors of differentsizes. As most of the computers are equipped with the DB9serial port version, all wiring examples on this website will use that connectoras a default.
If you want to use the example with a DB25, simplyreplace the pin numbers of the connector according to the conversion table below. RS232 DB9 to DB25 converterDB9 - DB25 conversion DB9DB25Function18Data carrier detect23Receive data32Transmit data420Data terminal ready57Signal ground66Data set ready74Request to send85Clear to send922Ring indicatorRS232 serial loopback test plugsThe following RS232 connectors can be used to test a serial port on your computer.The data and handshake lines have been linked. In this way all data will besent back immediately. The PC controls its own handshaking. The first test plugcan be used to check the function of the RS232 serial port with standard terminalsoftware. The second version can be used to test the full functionality ofthe RS232 serial port with Norton Diagnostics or CheckIt. DB9DB25Function1 + 4 + 6 + 96 + 8 + 20 + 22DTRCD + DSR + RI2 + 32 + 3TxRx7 + 84 + 5RTSCTSTesting occurs in a few steps.
Data is sent on the Tx line and thereceived information on the Rx input is then compared with the original data.The signal level on the DTR and RTS lines is also controlledby the test software and the attached inputs are read back in the software to see if thesesignal levels are properly returned.The second RS232 test plug has the advantage that the ring-indicator RI input linecan also be tested. This input is used by modems to signal an incomingcall to the attached computer.RS232 null modem cablesThe easiest way to connect two PC's is using an RS232 null modem cable.
The onlyproblem is the large variety of RS232 null modem cables available. For simpleconnections, a three line RS232 cable connecting the signal ground and receiveand transmit lines is sufficient. Depending of the software used, somesort of handshaking may however be necessary. Use theto find the right null modem cable for each purpose.
For a Windows 95/98/ME DirectCable Connection, the RS232 null modem cable with loop back handshaking isa good choice.RS232 null modem cables with handshaking can be defined in numerous ways,with loopback handshaking to each PC, or complete handshaking betweenthe two systems. The most common null modem cable types are shown here.
RS-232 vs RS-485RS-232 and RS-485 are two standards for electrical transmission that predated modern computers. And despite their age, they are still pretty much in use today. The main difference between the two is the number of wires that they use. RS-232 uses 9 distinct wires; although some connectors, like the DB25, have more pins; the extra pins are unused and are just connected to ground. On the other hand the RS-485 only uses 3 wires; 2 for transmission and 1 for the common ground. The use of fewer wires means that the RS-485 is more cost effective than the RS-232 as there is less expense on the wiring.One of the RS-232 is that it is already full duplex compliant. RS-485 can only operate at half duplex unless a second set of wires is employed so that one set is used for transmitting and the other is used for receiving.There is also a difference between the RS-232 and the RS-485 when it comes to the voltages that they use.
The RS-485 only uses positive and negative 5V to create a voltage differential which the then recognizes as ones and zeros. On the other hand, the RS-232 recommends transmission voltage ±12V, although the maximum is at ±15V.
The voltage level can deteriorate to as low as ±3V at the receiving end and still be understandable to the receiver.Another advantage of the RS-485 is its excellent range. A single RS-485 link can reach up to 4,000ft. In comparison, the RS-232 cables have a typical range of 50ft. With the use of specialized cables, the range of the RS-232 cables can be extended but only up to 1,000ft. Or roughly 300m.Although both these electrical transmission standards were not intended for the industry, they’ve seen some wide use at one point or another. RS-485 was once used with SCSI and RS-232 was a common interface for modems, keyboards, mice, and many other computer peripherals.
Nowadays, RS-232 is already obsolete and being phased out in favor of other standards like USB and Firewire. But many computers still have an RS-232 port for compatibility purposes. RS-485 is also being phased out in computer hardware but has enjoyed wide use in other electronic devices; an example of which is in controlling CCTV cameras.Summary:1.RS-232 uses 9 wires while RS-485 only uses 3.2.RS-232 is full duplex while RS-485 is half duplex.3.RS-232 operates at ±15V while RS-485 only operates at ±5V.4.RS-485 has a longer range than RS-232.5.RS-232 is more common in computers than RS-485.