36 pin D-SUB female connector at the drive port, viewed from rear.
The Amstrad CPC6128 Plus, released in 1990 as the successor to the CPC6128, provides a 36-pin Centronics female socket for connection of an external floppy disk drive. The interface is derived from the Shugart Associates double-density MFM floppy bus, but the pin numbering differs from both the original Shugart standard and the earlier CPC6128 34-pin edge connector, so a re-pinned cable rather than a simple plug adaptor is required to connect a standard CPC drive. All even-numbered pins carry ground, whilst odd-numbered pins carry the active signals. Amstrad did not release an official external drive for the Plus range; the socket was intended for use with third-party or adapted CPC drives.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | n/c | - | Not connected |
| 3 | n/c | - | Not connected |
| 5 | n/c | - | Not connected |
| 7 | NINDEX | ? | |
| 9 | n/c | - | Not connected |
| 11 | NDSEL1 | ? | |
| 13 | n/c | - | Not connected |
| 15 | NMOTOR | ? | |
| 17 | NDSEL | ? | |
| 19 | NSTEP | OUT | Step head |
| 21 | NWDATA | OUT | Write Data |
| 23 | NWGATE | OUT | Write Gate |
| 25 | NTK00 | IN | Track 00 |
| 27 | NWRPT | IN | Write Protect |
| 29 | NRDDTA | IN | Read Data |
| 31 | NSIDE1 | ? | |
| 33 | NREADY | ? | |
| 35 | n/c | Not connected |
Notes
- Direction is Computer relative Diskdrive
- All even pins are GND, Ground
- The connector is a 36-pin Centronics female socket, not a D-sub, despite the image label
- Pin 1 on the CPC6128 Plus corresponds to wire 2 of a Shugart-compatible cable; wire 1 of a standard Shugart cable has no equivalent pin on this connector (hence pin 1 is not connected)
- The pin numbering was changed relative to both the standard CPC6128 34-pin edge connector and the Shugart standard; an adapted or re-pinned cable is required — a plug adaptor alone is insufficient
- The CPC464 Plus (sister model) omits the second drive connector entirely
- The floppy disk controller is an NEC uPD765-compatible device (FDC9216BT); the system supports a maximum of two drives total
Signals
- NINDEX — Index pulse input from drive (once per revolution); active low; Input
- NDSEL1 — Drive 1 select output from computer; active low; Output
- NMOTOR — Motor on output from computer; activates drive spindle motor; active low; Output
- NDSEL — Direction/drive select control output; active low; Output
- NSTEP — Step pulse output; each pulse moves the read/write head by one track
- NWDATA — MFM write data output to drive
- NWGATE — Write gate output; enables write current in drive head
- NTK00 — Track 00 input; asserted when head is positioned at track zero
- NWRPT — Write protect input; asserted when inserted disc is write-protected
- NRDDTA — MFM read data input from drive
- NSIDE1 — Side 1 select output; selects upper or lower recording surface; Output
- NREADY — Drive ready input; asserted when drive motor is up to speed and a disc is present; Input
References
- Amstrad CPC6128 Service Manual (1985) — Amstrad Consumer Electronics, Internet Archive