Date   : Thu, 23 Aug 2007 14:15:37 +0100
From   : dl.harper@... (David Harper)
Subject: M512 copro schematics?

Jules Richardson wrote:
>> Let me know when you finish tracing the '286 board.  I keep meaning to
>> try to debug what's wrong with the ones I have.
>
> It's a substantially different animal to the 80186 board it seems...
>
> ...
>
> Far as I know the '286 board pre-dates the Master 512 (as the '286 boards
> proved too expensive to rework for that machine), which probably explains 
> the
> complexity - I guess they managed to sort out all the niggles by the time 
> the
> 80186 board came along. (Also explains why these boards would run with 
> only
> 256K of memory when the M512 had twice that)

There are a few odd things they did with the 80186 board to make it work as 
the M512. (One such is the connection between the output of one of the 
chip's internal clocks and the NMI input. It took me ages to work out what 
this was for, but it turns out to be essential in preventing a lot of PC 
programs locking up as soon as they try to display anything on the screen.)

Similar things would have to be done with the '286 to get it to work as 
required. I suspect too much time would need to be invested to make it worth 
while.

David Harper