The X1541 is a PC-transfer cable designed by Leopoldo Ghielmetti (© 1992) that connects a PC’s 25-pin parallel port (SPP or PS/2 mode only — ECP/EPP modes are not compatible) to the Commodore serial bus via a 6-pin DIN 45322 connector, enabling data transfer between a PC and Commodore 1541 or 1581 disk drives. The Commodore serial bus is a bit-banged, open-collector, active-low protocol adapted from the IEEE-488 parallel bus; its DIN connector carries five active signals — SRQ, ATN, CLK, DATA, and RESET — plus a ground return. The cable exploits the open-collector nature of both buses by mapping the four driven DIN signals directly to four control output lines of the PC parallel port, with maximum recommended cable length of two metres.
25 PIN D-SUB MALE to the PC
6 PIN DIN (DIN45322) MALE to the Commodore drive
| PC parallel pin | PC signal | DIN pin | DIN signal |
|---|---|---|---|
| 18–25 | GND | 2 | GND |
| 1 | STROBE | 3 | ATN |
| 14 | AUTOFEED | 4 | CLK |
| 17 | SELECTIN | 5 | DATA |
| 16 | INIT | 6 | RESET |
Notes
- The PC parallel port must operate in SPP (Standard Parallel Port) or PS/2 bidirectional mode. ECP and EPP modes alter the electrical behaviour of the control lines and are not compatible with this cable.
- DIN pin 1 (SRQ — Service Request) is not connected.
- Maximum recommended cable length is two metres; use shielded four-wire or unshielded five-wire cable with a 6-pin male DIN 45322 plug and a 25-pin male D-SUB plug.
- All active signals on the Commodore serial bus are TTL open-collector, active-low.
Signals
PC parallel port (25-pin D-SUB male)
- GND (pins 18–25) — signal ground; connected to DIN pin 2
- STROBE (pin 1, active-low nSTROBE) — carries ATN (Attention) to the Commodore serial bus
- AUTOFEED (pin 14, active-low nAUTOFEED) — carries CLK (Clock) to the Commodore serial bus
- SELECTIN (pin 17, active-low nSELECT) — carries DATA to the Commodore serial bus
- INIT (pin 16, active-low nINIT) — carries RESET to the Commodore serial bus
Commodore serial bus (6-pin DIN 45322 male)
- SRQ (pin 1) — Service Request; not connected in this cable
- GND (pin 2) — signal ground; connected to PC parallel pins 18–25
- ATN (pin 3) — Attention; open-collector, active-low input to the 1541 drive; connected to PC parallel pin 1
- CLK (pin 4) — Clock; bidirectional open-collector; connected to PC parallel pin 14
- DATA (pin 5) — Data; bidirectional open-collector; connected to PC parallel pin 17
- RESET (pin 6) — Reset; active-low reset pulse; connected to PC parallel pin 16