DB25 Pinout
25-pin D-subminiature connector, the original EIA-232 serial pinout.
Overview
The DB25 (correctly DB-25) is a 25-pin D-sub originally specified by EIA/TIA-232 as the full RS-232 serial interface, with a top row of 13 pins and a bottom row of 12. It carries the primary data and modem-control signals plus a rarely used secondary channel and sync clocks.
Most equipment used only pins 2, 3, 7 and the handshake lines, which is why DE-9 supplanted it. The same shell is also the IBM PC parallel port, which has a different pinout - the RS-232 assignment is shown.
Pinout
| Pin | Name | Function | Description |
|---|---|---|---|
| 1 | PG / Shield | GND | Protective/frame ground |
| 2 | TXD | UART / DATA | Transmit data (DTE to DCE) |
| 3 | RXD | UART / DATA | Receive data (DCE to DTE) |
| 4 | RTS | SIGNAL | Request to send |
| 5 | CTS | SIGNAL | Clear to send |
| 6 | DSR | DATA | Data set ready |
| 7 | SG | GND / SIGNAL | Signal ground / common return |
| 8 | DCD | DATA | Data carrier detect |
| 9 | +V (test) | SIGNAL | Reserved (positive test voltage) |
| 10 | -V (test) | SIGNAL | Reserved (negative test voltage) |
| 11 | Unassigned | SIGNAL | Unassigned in most use |
| 12 | S.DCD | SIGNAL | Secondary carrier detect |
| 13 | S.CTS | SIGNAL | Secondary clear to send |
| 14 | S.TXD | UART / DATA | Secondary transmit data |
| 15 | TXC | CLK | Transmit clock (DCE source) |
| 16 | S.RXD | UART / DATA | Secondary receive data |
| 17 | RXC | CLK | Receive clock |
| 18 | LL | SIGNAL | Local loopback control |
| 19 | S.RTS | SIGNAL | Secondary request to send |
| 20 | DTR | DATA | Data terminal ready |
| 21 | RL / SQ | SIGNAL | Remote loopback / signal quality detect |
| 22 | RI | SIGNAL | Ring indicator |
| 23 | DSRD | SIGNAL / DATA | Data signal rate selector |
| 24 | TXC-DTE | CLK | Transmit clock (DTE source) |
| 25 | TI | SIGNAL | Test indicator |
Notes
- The same physical connector as an IBM PC parallel port, which uses an unrelated pinout.
- Most links use only pins 2, 3, 7 plus handshakes.
Reference: EIA/TIA-232 (RS-232) DB25 serial pinout· verified 2026-06-27