BOUNCE diy_efi: Admin request (fwd)

[Bill the arcstarter]

It was written:
>> 	I have come across a 28 pin prom that I just cant get a stable 
checksum
>> on. When I read it as a 27C128 I get FF in the bottom half of memory 
and
>> what looks like data in the top half. With the prom in its own 
circuit
>> pin 28 (VCC) is joined to pin 26 (A13) which would explain that they 
are
>> only looking for data in the top section of the prom and why the 
bottom
>> section is all FF. 

I agree.

>> 	The prom data lines "D0" to "D7" going to the MC68hc11 are all
>> reversed, "D0 goes to "D7", D1" goes to "D6" etc. This of course will

That's a sick trick.  Did they scramble the address pins too?  

Thats really nasty!

>> give the incorrect hex readings when the prom is read but what is
>> causing the checksum to be different on every read attempt?
>> 	I have made sure all the pins are very clean as I know from 
experience
>> this can cause different checksums.

Don't know.  c/sum should be the same if the same data is read each 
dump.  Perhaps you can record each data dump and look for a difference?  

Just a thought.

-Bill

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