The EIA 232D standard
The EIA 232D standard was developed in 1969 to specify the connections between a computer and a modem.
The term itself is an acronym which can be read as follows:
Electronics Industry Association (EIA) accepted standard, ID number 232 revision D
EIA 232D specifies the characteristics of the physical and electrical connections between two devices. Names and abbreviations are assigned to each pin or wire necessary for serial communications, for example:
| Signal | Equip. Type | Symbol | Pin |
|---|---|---|---|
| Transmit Data | DCE | TxD | 2 |
| Receive Data | DTE | RxD | 3 |
| Request to Send | DCE | RTS | 4 |
| Clear to Send | DTE | CTS | 5 |
| Data Set Ready | DTE | DSR | 6 |
| Signal Ground | SG | 7 | |
| Carrier Detect | DTE | CD | 8 |
| Data Terminal Ready | DCE | DTR | 20 |
| Ring Indicator | DTE | RI | 22 |
In EIA 232D, devices using pin 2 (TxD) for output (for example, computers and terminals) are given the name data terminal equipment (DTE). Devices using pin 2 (TxD) for input (for example, modems) are given the name data communication equipment (DCE).
EIA 232D also specifies the connectors. A DTE device normally has male connectors while DCE devices have female connectors. This standard is not always adhered to by manufacturers; therefore users should always review the device documentation before cable connection.