37 PIN D-SUB MALE at the DTE (Computer).
37 PIN D-SUB FEMALE at the DCE (Modem).
| Pin | Name | Direction | Description |
|---|
| 1 | | --- | Shield (V.24 101) (Ground) |
| 2 | SI | Output | Signal Rate Indicator (V.24 112) (Control) |
| 3 | n/a | --- | unused |
| 4 | SD- | Output | Send Data (A) (V.24 103) (Data) |
| 5 | ST- | Input | Send Timing (A) (V.24 114) (Timing) |
| 6 | RD- | Input | Receive Data (A) (V.24 104) (Data) |
| 7 | RS- | Output | Request To Send (A) (V.24 105) (Control) |
| 8 | RT- | Input | Receive Timing (A) (V.24 115) (Timing) |
| 9 | CS- | Input | Clear To Send (A) (V.24 106) (Control) |
| 10 | LL | Output | Local Loopback (V.24 141) (Control) |
| 11 | DM- | Input | Data Mode (A) (V.24 107) (Control) |
| 12 | TR- | Output | Terminal Ready (A) (V.24 108.2) (Control) |
| 13 | RR- | Input | Receiver Ready (A) (V.24 109) (Control) |
| 14 | RL | Output | Remote Loopback (V.24 140) (Control) |
| 15 | IC | Input | Incoming Call (V.24 125) (Control) |
| 16 | SF/SR+ | --- | Signal Freq./Sig. Rate Select. (V.24 126) (Control) |
| 17 | TT- | Output | Terminal Timing (A) (V.24 113) (Timing) |
| 18 | TM- | Input | Test Mode (A) (V.24 142) (Control) |
| 19 | SG | --- | Signal Ground (V.24 102) (Ground) |
| 20 | RC | --- | Receive Common (V.24 102b) (Ground) |
| 21 | n/a | --- | unused |
| 22 | SD+ | Output | Send Data (B) (V.24 103) (Data) |
| 23 | ST+ | Input | Send Timing (B) (V.24 114) (Timing) |
| 24 | RD+ | Input | Receive Data (B) (V.24 104) (Data) |
| 25 | RS+ | Output | Request To Send (B) (V.24 105) (Control) |
| 26 | RT+ | Input | Receive Timing (B) (V.24 115) (Timing) |
| 27 | CS+ | Input | Clear To Send (B) (V.24 106) (Control) |
| 28 | IS | Output | Terminal In Service (V.24 n/a) (Control) |
| 29 | DM+ | Input | Data Mode (B) (V.24 107) (Control) |
| 30 | TR+ | Output | Terminal Ready (B) (V.24 108.2) (Control) |
| 31 | RR+ | Input | Receiver Ready (B) (V.24 109) (Control) |
| 32 | SS | Input | Select Standby (V.24 116) (Control) |
| 33 | SQ | Input | Signal Quality (V.24 110) (Control) |
| 34 | NS | Output | New Signal (V.24 n/a) (Control) |
| 35 | TT+ | Output | Terminal Timing (B) (V.24 113) (Timing) |
| 36 | SB | Input | Standby Indicator (V.24 117) (Control) |
| 37 | SC | --- | Send Common (V.24 102a) (Ground) |
| Name | Description | Function |
| AA | Shield Ground | Also known as protective ground. This is the chassis ground connection between DTE and DCE. |
| AB | Signal Ground | The reference ground between a DTE and a DCE. Has the value 0 Vdc. |
| BA | Transmitted Data | Data send by the DTE. |
| BB | Received Data | Data received by the DTE. |
| CA | Request To Send | Originated by the DTE to initiate transmission by the DCE. |
| CB | Clear To Send | Send by the DCE as a reply on the RTS after a delay in ms, which gives the DCEs enough time to energize their circuits and synchronize on basic modulation patterns. |
| CC | DCE Ready | Known as DSR. Originated by the DCE indicating that it is basically operating (power on, and in functional mode). |
| CD | DTE Ready | Known as DTR. Originated by the DTE to instruct the DCE to setup a connection. Actually it means that the DTE is up and running and ready to communicate. |
| CE | Ring Indicator | A signal from the DCE to the DTE that there is an incomming call (telephone is ringing). Only used on switched circuit connections. |
| CF | Received Line Signal Detector | Known as DCD. A signal send from DCE to its DTE to indicate that it has received a basic carrier signal from a (remote) DCE. |
| CH/CI | Data Signal Rate Select
(DTE/DCE Source> | A control signal that can be used to change the transmission speed. |
| DA | Transmit Signal Element Timing
(DTE Source) | Timing signals used by the DTE for transmission, where the clock is originated by the DTE and the DCE is the slave. |
| DB | Transmitter Signal Element Timing
(DCE Source) | Timing signals used by the DTE for transmission. |
| DD | Receiver Signal Element Timing
(DCE Source) | Timing signals used by the DTE when receiving data. |
| IS | terminal In Service | Signal that indicates that the DTE is available for operation |
| NS | New Signal | A control signal from the DTE to the DCE. It instructs the DCE to rapidly get ready to receive a new analog signal. It helps master-station modems rapidly synchronize on a new modem at a tributary station in multipoint circuits |
| RC | Receive Common | A signal return for receiver circuit reference |
| LL | Local Loopback / Quality Detector | A control signal from the DTE to the DCE that causes the analog transmision output to be connected to the analog receiver input. |
| RL | Remote Loopback | Signal from the DTE to the DCE. The local DCE then signals the remote DCE to loopback the analog signal and thus causing a line loopback. |
| SB | Standby Indicator | Signal from the DCE to indicate if it is uses the normal communication or standby channel |
| SC | Send Common | A return signal for transmitter circuit reference |
| SF | Select Frequency | A signal from the DTE to tell the DCE which of the two analog carrier frequencies should be used. |
| SS | Select Standby | A signal from DTE to DCE, to switch between normal communication or standby channel. |
| TM | Test Mode | A signal from the DCE to the DTE that it is in test-mode and can't send any data. |
| | Reserved for Testing | |
