David Gesswein's MFM emulator on the DEC Professional

Paul Koning paulkoning at comcast.net
Sun Jan 17 12:35:44 CST 2021

> On Jan 16, 2021, at 5:32 PM, Paul Koning <paulkoning at comcast.net> wrote:
> I just completed a set of tests of David's MFM emulator on my Pro 380.
> Summary: everything works right.  Very impressive device.  My compliments to David for an amazing piece of engineering.
> Details: ...

Some more details.

1. I forgot to mention that the Pro disk controller always uses only drive select 1, so that has to be set as the primary drive select on P7, and nothing on the secondary (P8).

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.

3. Since on the RD50 drive select 4 is an output, you can't plug one of those drives into the emulator either for reading or writing, since the emulator (also) drives that pin.  You'd have to open up that wire or something along those lines to avoid having a battle between two drivers.


More information about the cctech mailing list