:: Area: #0 (BBC-Micro) Message: 55962 (Read 1 time, has 0 replies, 4578 bytes) Date : Tue Oct 25 01:01:14 2005 From : Pete Turnbull Subject: Floppy pinouts and twists Reply-To: bbc-micro@cloud9.co.uk Message-ID: <10510250101.ZM3400@mindy.dunnington.plus.com> It occurs to me that many readers won't have a mental picture of the pin assignments and twisted floppy cables we've been discussing, so here is a diagram: Pin BBC/SA400 IBM PC IBM PC Standard Drive Drive 2 (note 1) Density 4 In Use (unused) 6 DS3 (unused) 8 Index Index 10 DS0 ------- Motor0 --. .-- Motor1 -- MotorOn 10 \ / 12 DS1 ------- DS1 -. .---\-/---- DS0 --------- DS2 12 X X 14 DS2 ------- DS0 -' `---/-\---- DS1 --------- DS1 14 / \ 16 MotorOn --- Motor1 --' `-- Motor0 ------ DS0 16 18 Direction Direction 20 Step Step 22 Write Data Write Data 24 Write Gate Write Gate 26 Trk00 Trk00 28 Wr.Prot. Wr.Prot. 30 Read Data Read Data 32 Side 1 Side 1 34 Ready Disk Changed Pins 11, 13 and 15 are twisted too, but all odd-numbered pins are ground connections so the twist leaves them unaffected. Note 1: This is TG43, or "Track Greater Than 43" on some very old drives/interfaces; used to indicate that the drive should reduce the write current on the inner tracks. Most drives do this automatically and do not need this signal. A drive configured for a PC will have no connection to pins 10 or 14, but will have its drive select connected to pin 12 and its motor control connected to pin 16. Thus, when placed after the twist, it will appear to a PC as Drive A, and when placed before the twist, it will appear as Drive B. To a more conventional controller circuit, the drive would appear as Drive 1 (equivalent to B) when placed before the twist, but would not work as Drive 0 when placed after the twist, because the conventional controller would not activate DS2 and DS0 at the same time. However, if the drive were configured not to need the motor control signal, it might work as Drive 2. Some interfaces (including the BBC Micro) only implement DS0 and DS1, not DS2 and DS3. Some other interfaces only implement DS0...DS2, leaving DS3 (pin 6) unconnected. -- Pete Peter Turnbull Network Manager University of York