Field Controls 10 manual Serial interface, The RS-232c standard, The connections

Serial interfaces

Serial interface

In this part of the installation manual, you will learn some basics of serial communication, the hardware involved and how the CER controller connects to your RS- 232 device.

RS-232

The RS-232c standard

The RS-232 standard (RS stands for recommended standards) was published first in 1969 by the EIA (Electronic Industries Association). It was originally drawn up to specify the connections between terminals and modems. It specifies the electrical characteristics of circuits between the devices and gives names and numbers to the wires.

RS-232-C is the third - and most common - version of the standard so it is often simply referred to as RS-232 (without the 'c'). The combination of ITU-T's (formerly CCITT) V.24 and V.28 standards are equivalent to EIA-RS-232-C. In short: V.24+V.28 RS-232.

The characteristics of the RS-232c protocol are as follows:

Spoint-to-point communication (full duplex)

Smaximum line length between sender and receiver 15 meters (50 feet).

The connections

In serial communication, you'll encounter many references to the rather cryptic terms DTE (Data Terminal Equipment) and DCE (Data Communication Equipment). The word terminal indicates the end of the line, as in bus terminal. In the phrase data terminal equipment it means the extreme ends of the data communications circuit. The data communications equipment, modems for example, provide the communication between the two DTEs.

Terminal

Modem

RS-232c

DCE

DTE

TELEPH ONE NETWORK

Computer

Modem

RS-232c

DCE

DTE

The RS-232c pin-out

The 9-pin RS-232c connector is described in the EIA/TIA-574 standard.

See the chapter “Pin Assignments” for Hardware platform specific information about the pin-out.

CER International bv 23