John Robertson wrote:
> A NOP is a NOP. Simply hardwire a 24 pin header to the required
> configuration and install it in the boot ROM socket.
>
> It seems for a Z80 that all you have to do is remove the boot ROM and
> as long as the DATA lines are all pulled high then it will happily NOP...
>
Not exactly a NOP on your Z80 example, all data lines pulled high give
you a "restart 7" whick causes the processor to push the current address
onto the stack and then fetch the instrucion from the restart 7 vector,
which will be another "restart 7" command. So what you end up with is
one read cycle followed by two write cycle (the stack push). Since
you're now in a loop you continually push, two bytes at a time, the same
address data to EVERY LOCATION IN THE ENTIRE MEMORY MAP! You're doing
writes even to ROM addresses!
It does work nice, though, for checking address lines since they all toggle.
ONLY reason I know that was due to work on an 8085 based weather radar
at my Real Job several years (OK, over a decade, happy?) ago.
>
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Received on Thu Jul 3 02:33:08 2003
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