HP LaserJet printers equipped with a serial interface use a standard RS-232C connection compliant with TIA/EIA-232-F. The printer side presents a 25-pin D-sub (DB-25) female connector, whilst the host or print-server side uses a 9-pin DE-9 (commonly called DB-9) male connector, following the EIA-574 standard for DTE equipment. HP supplied accessory cables (C2932A, DB-9 to DB-9, and C2933A, DB-9 to DB-25) for its LaserJet 4000 series and configured the interface for 9600 baud by default, with either DTR/DSR hardware or XON/XOFF software flow control selectable.
9 pin D-SUB male connector to the Intel Netport ExpressXL serial port
25 pin D-SUB female connector to the HP LaserJet printer serial port
| Intel Netport ExpressXL serial port Name | Intel Netport ExpressXL serial port Pin | Direction | HP LaserJet printer serial port Pin | HP LaserJet printer serial port Name | Description |
|---|---|---|---|---|---|
| DCD | 1 | ← | 4 | RTS | |
| RXD | 2 | ← | 2 | TXD | |
| TXD | 3 | → | 3 | RXD | |
| DTR | 4 | → | 5,6 | CTS,DSR | |
| Ground | 5 | 7 | Ground | ||
| DSR | 6 | ← | 20 | DTR | |
| RTS | 7 | → | 8 | ||
| CTS | 8 | ← | 20 | DTR |
Notes
- The DB-9 connector on the host/print-server side follows EIA-574 (DTE pinout): Pin 1 = DCD, Pin 2 = RxD, Pin 3 = TxD, Pin 4 = DTR, Pin 5 = Signal Ground, Pin 6 = DSR, Pin 7 = RTS, Pin 8 = CTS.
- The DB-25 connector on the HP LaserJet printer side follows TIA/EIA-232-F (DCE/printer pinout): Pin 2 = TxD, Pin 3 = RxD, Pin 4 = RTS, Pin 5 = CTS, Pin 6 = DSR, Pin 7 = Signal Ground, Pin 20 = DTR.
- RS-232C signal levels per TIA/EIA-232-F: logic 1 (mark) = −3 V to −15 V; logic 0 (space) = +3 V to +15 V.
- Maximum recommended cable length is limited by the 2500 pF load capacitance specification of TIA-232-F, giving approximately 15 m at 20 kbps with standard cable.
- DTR from the printer (DB-25 pin 20) is wired to both DSR (DB-9 pin 6) and CTS (DB-9 pin 8) on the print-server side, a common loopback arrangement used when the host does not drive independent handshake lines.
Signals
- DCD — Data Carrier Detect; input to the print server, driven by printer RTS.
- RXD — Receive Data; serial data received by the print server from the printer TxD line.
- TXD — Transmit Data; serial data sent from the print server to the printer RxD line.
- DTR — Data Terminal Ready; output from the print server, looped to printer CTS and DSR to indicate the host is ready.
- Ground — Signal ground common to both sides.
- DSR — Data Set Ready; input to the print server, driven by printer DTR to signal the printer is online.
- RTS — Request to Send; output from the print server to the printer; printer-side destination not documented.
- CTS — Clear to Send; input to the print server, driven by printer DTR for flow control.
References
- HP LaserJet 4000 Series User’s Guide — Hewlett-Packard Company; Appendix A-16 details serial cable specifications for cables C2932A and C2933A
- Popular Connector Pin Assignments for Data Communications, SNLA039 — Texas Instruments; TIA/EIA-232-F and EIA-574 DB-9/DB-25 standard pin assignments