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Re: Using a 4pin crystal with an old 6502
Posted: Fri Jan 24, 2020 10:16 am
by drogon
It's all true - but note that it's the max cycle time which is the constraint here. The general advice is to go no slower than 100kHz for reliable operation. In practice you've probably got some tens of milliseconds before charge leakage starts to flip values, maybe more: for manual experimentation this is no big deal, but reliable operation in the field is another matter. And if you're trying to debug something, you don't want an extra source of uncertainty!
Off at a slight tangent, but once upon a time a company I was working at wanted to characterise some of the memory SIMs (and other shaped modules) they were making[1] so we built a test rig for DRAM that did all the refresh in software (From a transputer). I recall some of them being very reliable in the small number of seconds range but typically if you didn't refresh them at least once a second then you'd be in trouble.
-Gordon
[1] There was a shortage of 32-pin SIM modules in the early 90's so this company made their own - even sold them for a while too
Re: Using a 4pin crystal with an old 6502
Posted: Fri Jan 24, 2020 6:15 pm
by BillO
Was Rockwell still manufacturing NMOS on the 45th week of 2011? Or am I reading something incorrectly ...
Not likely.
The only people making semiconductors in Mexico for some years now are Infineon and NXP. However, NXP do own some of Rockwell's IP through it's purchase of part of Conexant, so who knows?
Re: Using a 4pin crystal with an old 6502
Posted: Wed Jan 29, 2020 4:03 pm
by kazzie
But I see people running 6502s at 750 KHz all the time, so perhaps the data sheet is a bit conservative?
Those people include owners of the
Microtan 65, a 1979 machine that was designed to run at 750kHz (because they wanted a CPU speed that was a subdivision of the 6MHz clock they needed for their teletext-based display circuit, and they couldn't do 1.5MHz as there weren't any 6502s rated faster than 1MHz at the time).