[Techtoolslist] Ram Diagnosis Help Needed

[John Robertson]

John Robertson wrote:

> Mark Hooks wrote:

>> I'm trying to learn more about how to interpret RAM read/write test  

>> results

>> on Atari 6502 based games. Can someone recommend a good text book 

>> where I

>> can learn more about how to sort out high from low bits ? The Atari 

>> Cat Box

>> manual assumes you have this basic knowledge.... which I don't.  I've

>> searched the archives and the FTP site to no avail.

>>

>>  

>>

>> Mark Hooks

>>

>>

>>   

>

> High RAM is data bits 4 - 7, Low RAM is data bits 0 - 3.

>

> Try this with the CAT box when it says there is a RAM error - write a 

> memory location with "AA" then read it. Should be "AA" of course. then 

> try writing "55" and reading that back.

>

> OK, so, lets say AA worked fine(10101010) but 55  (01010101)gave back 

> 45 (01000101). This would mean that  the Low RAM has a stuck bit (Low 

> at that memory location) on data line 3. This is a VERY basic RAM 

> test, but gives you the idea of how RAM tests.

>

> There are many web pages on RAM testing and the algorithms used, 

> fascinating reading!

>

> John :-#)#

>

Ah, right, can't count...the error is on data bit 4, not 3...you count 
from the right to left from least to most significant digit.

John :-#(#

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