Re: 8088 and 610 saga continues...

From: Michał Pleban <>
Date: Sun, 30 Jan 2011 22:02:15 +0100
Message-ID: <>

W dniu 2011-01-30 19:43, Michał Pleban pisze:

> But I observed, that memory corruption does not happen until we start executing this instruction:
> F000:F0BD	mov al, 44h
> F000:F0BF	out 21h, al
> F000:F0C1	nop
> This instruction is a signal to the *6509* to start sending reply bytes.
> When it is executed, memory corruption happens. Why this particular
> instruction? I have no idea... :-(

Coincidentally, when 8088 is executing these instructions, 6509 is just
around this code:

$FDA0	jsr $FDEE

which has $A1 as the address of one of its bytes. Until then, no kernal
instruction is executed from $xx21 nor $xxA1 locations when handling the
IPC call. Maybe the coexistence of $A1 on the 6509 bus and $21 on the
8088 causes the problem? But that's just pure voodoo...


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Received on 2011-01-30 22:00:19

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