Mexican CPUs

[Tickled_Pink]

I seem to recall people muttering about potential problems with 6502 processors made in Mexico. Do the issues involve it not having enough oomph to drive the PBI bus properly or something?

 

Just been digging through my collection. Of the first three machines I opened, two had Mexican processors and the other (which isn't working - my original from 1985) has one with different markings.

 

Can someone explain what the issues with the Mexican CPUs actually are?

[classics]

I believe the issue is drive strength. The CPUs cannot drive the number of TTL loads specified in the rockwell datasheets without the bus voltages dropping very badly. Noise also becomes much more of an issue as the voltage goes down, so computer with these cpus can exibit seemingly really strange and random problems.

 

I have seen this with Synertek 6502 and a few rockwell 6502, but I didnt check to see if those were from south of the border.

[Tickled_Pink]

I believe the issue is drive strength.  The CPUs cannot drive the number of TTL loads specified in the rockwell datasheets without the bus voltages dropping very badly.

 

As I said, not enough oomph

 

I've never actually experienced any problems with the Mexican processors. I read elsewhere that there is a problem with heat, as they don't work so well when they get hot. Here in Wales, that hardly ever becomes an issue

 

One of the systems I have is highly upgraded with 256K, a Pokey stereo upgrade, second PIA and dual OS (2nd PIA used as a parallel printer port), plus other minor refinements (such as composite monitor jack and improved video).

 

Actually, while I'm typing this something has just crossed my mind. I did have problems with that machine at one point. Whenever the second OS was enabled I would receive bad characters on screen. The room I was using it in has a habit of getting pretty hot whenever the central heating was switched on. Tried the machine again yesterday in the kitchen, where it's much cooler, and it worked fine.

 

I suspect that much of the performance issues of the Mexican is related to the fact that it's out of spec where the operating temperature is concerned. If that is the case, I'm surprised they were allowed out of the factory.

 

Oh - and BTW: The two SIO2PC units I ordered off you earlier in the week arrived this morning. THAT'S SERVICE!