Here are some notes I made from a news group posting and a website Chuck mentioned:
Here is the pinout (from
http://fjkraan.home.xs4all.nl/comp/trs80m2/fixing.html)
These lines were terminated in the Disk Station, on the last drive in the cable (as it should):
TRS-80 MODEL II floppy drive terminator
Code:
50p. func. terminator pin
---+------+---+--------
2 | NC | > | 7 Low current
4 | NC | |
6 | NC | |
8 | NC | |
10 | | < | Two sided
12 | | < | Disk change
14 | SDSEL| > | Side select
16 | NC | |
18 | HLD* | < | Head load
20 | IP* | < | Index pulse
22 | RDY | < | Ready
24 | NC | |
26 | DS1* | > | 11 Drive select 1
28 | DS2* | > | 12 Drive select 2
30 | DS3* | > | 14 Drive select 3
32 | DS4* | > | 2 Drive select 4
34 | DIR* | > | 1 Direction select
36 | STEP*| > | 13 Step
38 | CPWD*| > | 15 Write data
40 | WG* | > | 10 Write gate
42 | TRK0*| < | Track 0
44 | WPRT*| < | Write protect
46 | RD* | < | Read data
48 | NC | |
50 | NC | |
These are all the signals from the disk controller to the disks. The signals to the disk controller are terminated on the disk controller board. All signals are open collector, meaning the high level is provided by the terminator, which is basically a resistor to Vcc. The low level is provided by the collector of a transistor switched on. The advantage is that multiple devices (read disk drives) can control the line.
The terminator in the Disk Station was more advanced, probaly to dampen reflections due to the long flatcable; 215 cm (or 85 inch). BTW, there is also a short cable to the internal drive;
Code:
+5V
|
+++
| |
| | 220 ohm
| |
+++
|
+--- signal
|
+++
| |
| | 330 ohm
| |
+++
|
GND
YMMV