Good haul of old pc stuph

[Chuck Guzis]

12/20/2005 at 10:45 PM Jim Leonard wrote:

>RAM checks out okay after 65536 pattern writes and reads.  So whatever is 
>making the single-bit errors I don't know -- it only happens in 320x200 
>graphics mode, and is fine elsewhere.  This is an original IBM CGA, not a
>clone.

That's what I was working from.  Have you tried doing a read of the display
every so often (without writing) and comparing to previous reads to see if
bits are getting picked/dropped?   That would settle the question of the
RAM.  I'm not sure if a read/write will find all problems.

The CGA wasn't a bad design, considering what was available, although I
wonder about using 74153's in U9/U10 rather than the LS or S parts.

Now the MDA was a mess--traces going nowhere, logic that went nowhere.
I've wondered if it was some incomplete design rushed to production.

Cheers,
Chuck