25 pin D-SUB female connector at the computer.
Sun workstations from the Sun-3 series (1988) onwards fitted a 25-pin D-sub female connector for each asynchronous serial port, wired as DTE and conforming to both RS-423 and RS-232-C. Earlier SPARCstation models such as the SPARCstation 2 and SPARCstation 5 exposed each serial channel on its own individual DB-25 socket; Port A carries full modem-control signals plus optional synchronous clock lines, making it suitable for synchronous as well as asynchronous operation. Signal voltages default to ±5 V (RS-423 mode) on most models, with ±12 V RS-232 available depending on the system and jumper configuration.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | n/c | - | |
| 2 | TXD | OUT | Transmit Data |
| 3 | RXD | IN | Receive Data |
| 4 | RTS | OUT | Request to Send |
| 5 | CTS | IN | Clear to Send |
| 6 | DSR | IN | Data Set Ready |
| 7 | GND | - | System Ground |
| 8 | DCD | IN | Data Carrier Detect |
| 9 | n/c | - | BUTTON_POR (Power-on reset) for Sun Ultra 80 / Sun Blade 1000 / Sun Blade 2000 / Sun Fire 280R / Enterprise 420R |
| 10 | n/c | - | BUTTON_XIR_L (Transmit internal reset) for Sun Ultra 80 / Sun Blade 1000 / Sun Blade 2000 / Sun Fire 280R / Enterprise 420R |
| 11 | n/c | - | +5 Vdc for Sun Ultra 80 / Sun Blade 1000 / Sun Blade 2000 / Sun Fire 280R / Enterprise 420R |
| 12 | n/c | - | |
| 13 | n/c | - | |
| 14 | n/c | - | |
| 15 | TRxC | IN | Transmit Clock |
| 16 | n/c | - | |
| 17 | RTxC | IN | Receive Clock |
| 18 | n/c | - | |
| 19 | n/c | - | |
| 20 | DTR | OUT | Data Terminal Ready |
| 21 | n/c | - | |
| 22 | n/c | - | |
| 23 | n/c | - | |
| 24 | TxC | OUT | Transmit Clock |
| 25 | n/c | - |
Notes
- The connector on the system unit is a female DB-25 (DE-26 shell), wired as DTE.
- This pinout applies to single-channel models (e.g. SPARCstation 2, SPARCstation 5) where each port has its own DB-25. The SS4/10/20/LX/Classic family uses a different, dual-port DB-25 that multiplexes ports A and B on one plug.
- Signal levels default to RS-423 (±5 V); many systems also support RS-232 (±12 V), sometimes selectable by jumper.
- Port A supports both synchronous and asynchronous operation; the clock pins (15, 17, 24) are only active in synchronous mode.
- Maximum baud rate on older models (e.g. SPARCstation SLC/ELC) is 19 200 bps transmit and 9 600 bps receive; later SPARCstation models support higher rates.
- Pins 9–11 carry system-management signals (power-on reset, XIR, +5 V) on certain later platforms (Sun Ultra 80, Sun Blade 1000/2000, Sun Fire 280R, Enterprise 420R) rather than standard RS-232 ring-indicator or secondary-channel functions.
Signals
- TXD — Transmit Data (DTE output); serial data sent from the workstation to the attached device.
- RXD — Receive Data (DTE input); serial data received from the attached device.
- RTS — Request to Send; asserted by the DTE to request permission to transmit.
- CTS — Clear to Send; asserted by the DCE to grant permission to transmit.
- DSR — Data Set Ready; indicates the modem or DCE is powered and ready.
- GND — Signal Ground; the common reference potential for all RS-423/RS-232 signals.
- DCD — Data Carrier Detect; asserted by the DCE when a carrier is detected on the line.
- DTR — Data Terminal Ready; asserted by the DTE to indicate it is ready for communication.
- TRxC — Transmit Clock input (synchronous mode); an external clock supplied to the UART to govern the transmit bit rate.
- RTxC — Receive Clock input (synchronous mode); an external clock supplied to the UART to govern the receive bit rate.
- TxC — Transmit Clock output (synchronous mode); a clock derived from the UART’s baud-rate generator, available to the attached DCE.