No standard was defined for null modem connections with RS232 and not long after their introduction, several different wiring schemes became common. Originally the standard was defined for DTE, data terminal equipment to DCE, data communication equipment connection, but soon people started to use the communication interface to connect two DTEs directly using null modem cables. The wiring of RS232 has always been a problem. Goals of the Yost serial wiring standard.Introduction in the Yost wiring standard.The "point of view" of the computer (DTE). The names: "receive" and "transmit" should be interpreted from The meaning of the pins are the same on both Data Terminal Equipment andĭata Communications Equipment. Nowadays computers used as DTE instead of a terminal. Initially, RS232 ports were used for connecting aĭumb terminal (DTE) to a modem (DCE). On the same wire but neither would be able to receive any ![]() If you will do it, then they would both send out signals Therefore, you can't connect two devices that can send data out (DTE-DTE connection) using a straight cable. Unable to receive any signal using this pin. For example, if pin #2 outputs data, then it is You can see examples in the " SerialĪll signals of the RS232 port is are unidirectional. There are several cable layouts possible. Two DTE devices (for example, two computers or a computer and an external device). It is possible two connection types between serial ports: straight (pins 2 on both sides are connected) or null-modem (pin #2 is connected to pin #3 on another side).įirst connection type is used between DTE (Data Terminal Equipment) and DCE (Data Communications Equipment) devices (for example, a computer and modem), and the second connection type is used between How to connect RS232 ports using cablesĪ serial port is used to connect devices or computers, and therefore it should be connected to another serial port.Īn external device or modem that is connected to the serial port has an identical built-in serial Serial Port Monitor software can work with all signal of the RS232 interface. It is possible for all the 6 signal wires, but usually in standard devices these signal pins are used as described in the table above. In other cases the modem may not handle this signal or do something else when DTR is LOW (-12V). For example, a modem can hang up the telephone line when DTR is LOW. 3V)įor example, Advanced Serial Port Monitor can automatically control the DTR signal and set it LOW (-12V) when sends data out.Ī modem (or another device) that receives thisĭTR signal on another side (if these pins are connected) may do various things. RS232 uses following voltages for signals: ITU V.24 (pins description and names) and V.28 (electrical). RS232 defines both the physical andĮlectrical layers of this interface. ![]() Telecommunications Industry Association) issued several RS232 standards. This is defined by the hardware interface and you can't change it.īut all other pins can be controlled by a software and can be used for other tasks (rarely). Only 3 pins of the 9 have a fixed meaning: send, receive and signal Note: DCD can be sometimes labeled as CD Port Pins May Have No Constant Meaning
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