B&B Electronics RS-422 manual RS-232 Connections/Operation, RS-232 Operation, RS-232 Pinouts

Chapter 5: RS-232 Connections/Operation

The DB-9 male connector is configured as a standard RS-232 (DTE) serial port. Table 3 shows the signal names and pin numbers.

Table 3: RS-232 Pinouts

RS-232 Operation

RS-232 signal lines are referenced to Ground, and each signal can alternate above and below ground by the rated voltage (see Specifications for RS-232 Transmitter/Receiver). Typical input voltage levels range from –11 to –3 Volts or +3 to +11 Volts.

The primary RS-232 signals are Transmit (Tx) and Receive (Rx), so together with Ground, they make a “3-wire” interface.

The RTS and CTS signals are Handshaking lines used to indicate to the other device that data can be sent or received. These lines may be enabled or disabled on a byte-by-byte basis and are used to prevent buffer overrun or the loss of data.

Two secondary Handshaking signals are DTR and DSR. They are usually enabled when the device is powered up and the port is open. They may be used for flow control by some devices instead of RTS and CTS.

DCD is used by a modem to indicate Carrier to the computer so data can be sent/received. RI is output by a modem to indicate that the phone or FAX line has a incoming call, so it can be handled.

B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 B&B Electronics Ltd – Westlink Comm. Pk. – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445