David Gesswein's MFM emulator on the DEC Professional

Fred Cisin cisin at xenosoft.com
Sun Jan 17 13:12:25 CST 2021

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.

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 

But, on most machines after that, pin 32 is SIDE SELECT.  It is used to 
access side B of the drive.

On some drives, pin 34 was "DRIVE READY"/"DISK CHANGE"

Grumpy Ol' Fred     		cisin at xenosoft.com

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