I thought I would summarize a somewhat meandering thread.
I¡¯ve received the Artek manual and it is great!?
It appears I do have a failing ROM IC.?
As time went by HP changed from 4 4k*8 chips to 2 8k*8 chips and there is a way to jumper some boards to tell it which is installed.? (Joe: is that just the A/B jumpers near U5, or is it more than that?).? Apparently there are even some 3325a¡¯s with 3 ROM ics.
The HP nano-processor only has 11 address lines for a 12 bit space and so they played games to extract the 12 bit.? In the 4-chip solution, each chip has 2 select pins which are used in such a way as to provide the top 2 most significant bits.
Thus far, I have not found a 4k*8 EPROM or EEPROM that is pin-compatible with the original Synertek Sy2332/Motorola MCM88A332 masked ROM.? The TMS2532 are almost right, but lack the second select pin. [I keep seeing this listed even in historical literature as pin-compatible, but it is not according to the data sheets.? I¡¯ve seen this so many places that I wonder if the datasheets are wrong and pin 20 can be used as a second select.]
The original 2-IC solution used the Motorola MCM68764C EEPROM.? A later version of that chip? is the Motorola MCM68766.? Joe has previously extracted the 2-IC ROM program.? I would guess that the 4-IC data is the same, just split between chips.? I also think the data is the same independent of options as otherwise the signature analysis info would have to change between machines, and it does not.
My repair options include:
4 IC¡¯s.? This looks to require some extra glue logic to decode the second select unless a pin-compatible EEPROM can be found.? It would also require me to extract my data or split the existing 2-IC data.
2 IC¡¯s.? This only requires some jumper changes and the ROM program is already available.
1 IC solution.? Because the 3325a already decodes the 2 select pins as if they¡¯re address pins, this would only require a simple pin-remapping board for the new IC.
Option B looks like the obvious choice except that I have so far only been able to find used replacement EEPROMs and I wonder about the longevity of those.
I¡¯d also like to help the next person that needs to fix the ROM in a 3325a, and that argues for Option C.? Once option C is chosen almost any parallel ROM can be used and I¡¯m seeing some flash-ROM with a listed lifetime of 100+ years.
Does anyone have a favorite 16k*8 EEPROM ic that is common and likely to be available for a few more years?
