[Techtoolslist] Data I/O Series 22 problem

[vector]

I purchased a Series 22.... and now that I've ruined 6 Harris 7641 
equivalent PROMs (minimum value about $15)... I've determined what the 
symptoms are I am seeing.

This is a 512 byte PROM.

I'm thinking A6 line to the PROM during read is either high or 
floating, as if you break the 512 byte range into 8 blocks of 64 bytes 
you should have

ABCDEFGH

When I read a good source rom in, I use edit and compare it against a 
known good hex dump, and I'm seeing

BBDDFFHH

with blocks A, C, E, and G missing.

This would seem to idnicate that the A6 line is high during read.

Unfortunately my MOD-EMUP which should handle these PROMs 49 times out 
of 50 (or so it seems) will read any 7641 or compatible as all FFs 
(which it probably ins't reading anything... and the FFs were part of 
the EMUP's software clear).

I think I read you can read these as a 2732 and the 512 bytes ends up 
repeated I think in specific positions in the read.... I have to google 
that again to see if during the writes, the A,C,E,and G blocks are all 0 
still like on a blank PROM.

I'm going to strip it down to look at the boards... and check first at 
the socket.

If that line is floating will I get this behavior, or only if it is 
driven high ?

Thanks,

-- Curt