David Gesswein's MFM emulator on the DEC Professional

Fred Cisin cisin at xenosoft.com
Sun Jan 17 13:54:04 CST 2021


Sorry about that.
I was, indeed, thinking of floppy drives (RX50), which could have their 
own pin 32 and drive select incompatabilities

>> On Sun, 17 Jan 2021, Paul Koning via cctalk wrote:
>>> 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.
>> On Jan 17, 2021, at 2:12 PM, Fred Cisin via cctalk <cctalk at classiccmp.org> wrote:
>> 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.
On Sun, 17 Jan 2021, Paul Koning 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

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