18 Jan
2016
18 Jan
'16
11:04 a.m.
On Mon, Jan 18, 2016 at 10:13 AM, tony duell <ard at p850ug1.demon.co.uk>
wrote:
IF the PC100-A is like the PC100-B (which I have full
schematics for)...
Yes, the 8088 is expected to load Z80 program and take it out of reset. The
only
interrupt wired to the z80 is the software interrupt from the 8088.
All LEDs on, means, "replace the system
board".
I'm not sure, he wanted to hear that ;-)
And it's not even right!. You can have all LEDs on with a perfectly good
system board. A fault in the power-OK circuit in the PSU could cause it!
OK. As has been suggested the LEDs are turned on when the hardware is
reset (they are simply connected between the outputs of TTL latches and
+5V,
said latches are reset to 0 by the hardware reset signal) and then
controlled by
the processors. So all on suggests the processors are not running. Half of
the
LEDs are controlled by the 8088, the other half by the Z80. The 8088 is
reset by
the hardware reset signal, one of its output ports controls the Z80 reset
line.
So it is likely that the 8088 (at least) is not
running. I would start
there. Check its
reset and clock inputs, does it seem to be accessing memory, etc.
Check its address and data bus too...
Warner