Re: Gottlieb / Q*bert scripts for the 9010A/9100

Okay, a checksum on a single byte of FF yeilds an FF

I found this to be interesting......

Byte 0 = F3 Sig = FE
Byte 1 = 3E Sig = 1EE8
Byte 2 = 00 Sig = 1EE8
Byte 3 = ED Sig = 225A
Byte 4 = 47 Sig = 56B6

It isn't using the last read byte as the divisor is it?

Kev

>
>"Rom Signature is a four-digit HEXADECIMAL number that is a shorthand
>representation of the data obtained in an area of ROM memory. The ROM
>signature is obtained by successively dividing the data in ROM by a binary
>number (they DON't say what the @!$%#$@% number is! - JR). The resulting
>signature identifies the data from which it is obtained, and provides a
>convenient way of" (....blah blah, no other description of the process)."
>
>John :-#)#
>
>At 12:14 AM 09/05/2002 +0100, Phillip Eaton wrote:
>
>
>> >
>> > Just for the fun of it I wrote a quick program that tried all
>> > possible feedback
>> > combinations for 16 bit CRCs (65536 combinations), none of them
>> > generated the
>> > proper signatures, so it's more than just a variation of the standard
CRC
>> > calculations.
>>
>>Ah-ha! BUT!! Did you try for all possible combinations of /starting/ CRC?
>>Try that 'just for fun' - it should only take 65536 times as long :-)
>>
>>In my old serial comms days, we always started our CRC's at some bizarre
>>number (3403 IIRC), for two reasons 1) it offered better data security of
>>our protocols and 2) because it was safer to start there as some random
>>numbers are better generators than others.
>>
>>If you run a mathematical random number generators over a long period then
>>you get less random bits that others (i.e. the numbers stay about the same
>>for a while). This is the same for CRC's and thus the safety of the
>>calculation in spotting single or double bit errors is dimished in certain
>>areas.
>>
>> > Anybody know of two different ROMs, or byte streams that result
>> > in the same
>> > signature?
>>
>>There's loads in ROMIdent - just run with a bunch of EPROMS from your MAME
>>directory, and you're bound to find a couple.
>>
>>Cheers,
>>Phillip Eaton
>
>
Received on Wed May 08 17:54:23 2002