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Re: 80386 CPU Board

Hi Gary,

WRT the problem transfering back to the 'Z80' make sure you have placed a jumper on P36 pins 1-2.
The on-board master/slave transfer circuitry is based around D type flip/flop U91A and buffered by U49B this in turn is connected to P36 pin 1 and its pull up resistor, the jumper 1-2 is needed to enable the transfer back to the Z80 via this on-board circuit.

If you are using a S100 system monitor board then the above may not be relevant.

If all else fails check all your jumpers very carefully.

Also note my previous post (couple of weeks ago) regarding possible false triggering of a Z80 transfer, the fix has worked fine for me.


David Fry

On Sunday, February 1, 2015 at 4:24:54 PM UTC, Gary Kaufman wrote:
I completed the 80386 board yesterday, and after some confusion (on my
part) getting the monitor configured and jumpered correctly on the
MS-DOS support board it's running nicely at 32mhz using an AMD 80386-33

I'm running into two issues, and wonder if anyone has encountered them.

When I try to return to the Z80 using the "Z" command it hangs.

I've tried using a TX486DLC/E-33GA but it hangs after printing the
initial monitor prompt  (at both 16 and 32mhz).


- Gary