Re: [stella] 7800 programs -- potential problems?

Subject: Re: [stella] 7800 programs -- potential problems?
From: Keith Gerdes <kwg@xxxxxxxxxxxx>
Date: Wed, 19 Jan 2000 09:34:11 -0600
Kevin Horton wrote:
> I call it the "ROMblaster" because it does just that- blasts the ROM in the
> 7800 and temporarally over-powers it enough to get its reset vectors in
> and totally bypass the 7800's ROM by overpowering it.
> Circuit can be composed of a 74HC244 (enough "oomph" to overcome the cheesey
> ROM's output stage) and some selection logic to detect the proper memory
> range and force our code there, overpowering whatever is in the 7800.
> Note this overpowering lasts only several microseconds... not enough to damage
> anything or even get the chips hot.  Just long enough to switch the 7800's
> BIOS ROM out... about 3 lines of code (and a reset vector).

I inquired about doing something similar in 12/98 and the
feedback was "don't do it".  "Two devices outputting data
on the bus at the same time would cause damage no matter
how short of duration."

So how does Kevin's proposal differ?  :-)

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