Hi Guy's,
Just come across to this site while researching an old 7 segment LED, unfortunately I didn't find the information.
However maybe there is someone who may be able to suggest some advice to my new question.
I want to debug an Old 6502 computer which is no longer working and think a single step circuit for the 6502 chip would be of some use to me.
Does anyone have Experience with the 6502 CPU and could provide a Single Step Circuit.
Thanks
Bigmalc40
A youtuber, Ben Eater has a whole channel dedicated to building 6502 kits. I remember he made a clock circuit which would allow advancement of the program counter via a push button.
https://www.youtube.com/c/BenEater/featured (https://www.youtube.com/c/BenEater/featured)
Hi Count, Thanks for responding to my post, I don't know what you mean by "a modern CMOS version of the 6502, which has a completely static core", What is this?
The old 6502s, like, say, the stock ones you might find in an Apple II or a Commodore 64, cannot do this; they must be supplied a clock of a minimum frequency, or they will misbehave and exhibit unpredictable behaviour. I can't remember the exact minimum frequency, but IIRC it's at least several kHz.The original 6502 core used registers that were a lot like DRAM, and required regular refresh, just like DRAM. However, these cores had to be refreshed a lot more often than DRAM. I think the 6502 was similar to the 6800, and the 6800 needed a clock of at least 100kHz.
The normal 6502 way to do single-stepping would be to have the program to be debugged loaded in RAM.That is the approach a lot of early MPU evaluation boards used. Most instruction sets have some kind of software interrupt instruction which can be used in that way.
Setting a breakpoint would invoke the Monitor (no, not a CRT/LCD screen, but the resident ROM program) to insert a "BRK" instruction at the relevant location, which would then allow the user to examine the CPU registers and data involved.
Yep, and the only way you can do it with NMOS (and early CMOS) processors.There were some dynamic MPUs with specific single step hardware features. You had to keep the clock running with all dynamic MPUs, but that didn't mean instruction processing had to continuously proceed.
The old 6502s, like, say, the stock ones you might find in an Apple II or a Commodore 64, cannot do this
Apple II 64,700
Apple II Plus 545,500
Apple //e 4,250,000
Apple //c 450,000
Apple //c Plus 200,000
Apple IIGS 979,000
Total 6,489,200
Hi Guy's,
Just come across to this site while researching an old 7 segment LED, unfortunately I didn't find the information.
However maybe there is someone who may be able to suggest some advice to my new question.
I want to debug an Old 6502 computer which is no longer working and think a single step circuit for the 6502 chip would be of some use to me.
Does anyone have Experience with the 6502 CPU and could provide a Single Step Circuit.
Thanks
Bigmalc40