17 Jan
2021
17 Jan
'21
11:19 a.m.
On Jan 17, 2021, at 2:12 PM, Fred Cisin via cctalk
<cctalk at classiccmp.org> wrote:
On Sun, 17 Jan 2021, Paul Koning via cctalk wrote:
You seem to be talking about floppy drives. The MFM emulator deals with hard drives, and
the RD50 I mentioned is a hard drive (sold by DEC, 5 MB, the original hard drive for the
PDP-11 base Professional series).
paul
2. RD50s are odd; they use pin 32, which is
normally drive select 4, as an output to indicate "I am an RD50". The software
looks for that signal. So to emulate an RD50, install the jumper for drive select 4
(alongside the one for drive select 1) on P7.
Unimportant NIT:
On most drives, pin 32 is side select.
On TRS80 [Model 1], which had single sided drives, pin 32 was the fourth drive select.
(10, 12, 14, 32) The cable connectors had missing pins for three of those four, and the
drive was jumpered to respond to all four. Using four drives AND adding double sided
support required some modifications.
But, on most machines after that, pin 32 is SIDE SELECT. It is used to access side B of
the drive.