Date   : Sun, 10 Dec 2006 07:33:55 -0000
From   : dl.harper@... (David Harper)
Subject: how can I test if the 1770 and 8271 disc interface

salahdin mahmud wrote:

> fROM PAST EXPERIENCE, A ROM MAY SEMM TO WORK PERFECTLY, CAN DO THE USUAL
> THINGS, BUT ITS WHEN YEARS DOWN THE LINE YOU NOTICE A PROBLEM EG A
> PARTICULAR PROGRAM MAY NOT WORK(JUST 1 FROM OVER 200)  OR THE CHECKSUM 
> GIVES
> A DIFFERENT VALUE.
>
> SO JUST BECAUSE A ROM APPEARS TO BE FINE, IT DOESN'T MEANT IT'S ACTUALLY
> ERROR FREE!

This may perhaps be true with ROMs - a single memory location might fail. (I 
cannot see that dropping it is likely to cause this damage, though, unless 
you dropped it hard enough to crack the casing, or dropped it onto something 
very hot or highly radio-active!)

But the point here is that the 1770 and 8271 are NOT ROMs. These are 
interface chips. (Of course they are controlled by the central processor 
running under the control of a ROM which is elsewhere in the machine. But 
they are not ROMs themselves.)

Because they are not memory chips, they do not have locations to check. A 
checksum is meaningless.

Chips like this can only be tested by running through all their facilities, 
and by far the best way is to see whether they actually do the job. The 
internal parts of these chips are highly dependent on one another, so it is 
very likely that if anything fails then the whole chip fails. So will it 
read and write disks? If it will, then it is OK. If it won't, then it is 
broken.

David Harper