RS-232C

 

RS-232C – What is RS-232C?

RS-232C is a long-established standard (“C” is the current version) that describes the physical interface and protocol for relatively low-speed serial data communication Networks between computers and related devices.

RS-232C is the interface that your computer uses to talk to and exchange data with your modem and other serial devices. RS-232C is the interface between your Communication networks and other communication networks.

RS-232 Mechanical Specification

The essential feature ofRS-232 is that the signals are carried as single voltages referred to a common ground on pin 7. In its simplest form, the RS-232:C interface consis;9’of only two wires for data and ground. The ground is the absolute voltage reference for all the interface circuitry, the point in the circuit from which all voltages are measured. Data on pin 2 of the DTE is transmitted, while the same data on pin 2 of a DCE (modem) is received data as shown in Figure.

Data is transmitted and received on pins 2 and 3, respectively. Data Set Ready (DSR) is an indication from the Data set (the modem or DSU/CSU) that it is on. Similarly, DTR indicates that the DTE is on. Carrier Detect (CD) indicates that carrier for the transmission data is on.

Pins 4 and 5 carry the Request to Send (RTS) and Clear to Send (CTS) signals. In most situations, RTS and CTS are constantly on the communication session. However, where the DTE is connected to a multi-point line, RTS is used to turn the carrier on the modem on and off. On a multi-point line, it is imperative that only one station is transmitting at a time. When a station wants to transmit, it raises RTS. The modem turns on carrier, typically waits a few milliseconds for carrier to stabilize, and raises CTS.

The DTE transmits when it sees CTS up. When the station has finished its transmission, it drops RTS and the modem drops CTS and carrier together.

3. DCEs transmit on pin 3 and receive on pin 2. When the modem is communicating with another modem, three essential links are established. These are:

1. DTE to DCE The DTE or terminal and modem or DCE talk to each other.

2. DCE to DCE The two modems on the link talk to each other. When a DCE to DCE connection is established the modem will send a connect message to the computer. The connect message specifies the computer about the baud rate being used by the two modems for communication.

In case of modems with dissimilar baud rate, the modem of higher baud rate is set to send the data at the same rate of the other modem using the computer’s communication program.

3. DTE to DCE The host computer talks with its modem.

The output signal level usually swings between +12v and,-12v. RS-232 is simple, universal, well understood and supported everywhere. However, it has some serious shortcomings as an electrical interface.