RS-232-D Signal Chart

DB-25 Connector

1FGFrame Ground
2TDTransmit Data
3RDReceive Data
4RTSReady to Send
5CTSClear to Send
6DSRData Set Ready
7SGSignal Ground
8DCDData Carrier Detect
9Positive DC Test Voltage
10Negative DC Test Voltage
11Not Assigned
12(S)DCDSecondary Data Carrier Detect
13(S)CTSSecondary Clear to Send
14(S)TDSecondary Transmit Data
15TCTransmitter Clock
16(S)RDSecondary Receive Data
17RCReceiver Clock
18LLLocal Loopback
19(S)RTSSecondary Request to Send
20DTRData Terminal Ready
21SQSignal Quality Detect
22RIRing Indicator
23DRSData Rate Selector
24XTCExternal Transmitter Clock
25TMTest Mode

DB-9 Connector

1DCDData Carrier Detect
2RDReceive Data
3TDTransmit Data
4DTRData Terminal Ready
5SGSignal Ground
6DSRData Set Ready
7RTSRequest to Send
8CTSClear to Send
9RIRing Indicator