I'm interested in "old" computer hardware; especially DEC equipment, 6502, and 6800. If you've got anything old that you would consider selling or trading, let me know. My "best" stuff is some PDP-8 and PDP-11 hardware; but I have some early 6502 stuff such as an 8K PET and an OSI 500.

Question: What is the earliest date code on a 6502 chip?
I read somewhere that the earliest chips had a serious flaw (I forget what it was)... how early does the chip have to be to be 'broken'?

Pete
saipan59@uswest.net

I couldn't tell you about date codes, but the 6502 was first introduced in September of '75 at the Wescon computer show at the St. Francis Hotel in San Francisco, with a purchase price of $25. The 8080 and 6800 were $375 at the time.

I've never heard of any serious initial bugs, although the 6502 had various problems that never got corrected. These were corrected in the 65c02, which came out seven years later. I was in school in a microcomputer hardware and assembly programming class in '82 when we heard the exciting news. We were working on Aim-65's. As you know, the 65c02 also has additional instructions and addressing modes, uses only a fraction as much power as the 6502, and is now available in much faster speeds.

What could have made the bugs extra bad at first was the fact that programmers had no previous experience to help figure out problems. One that comes to mind is the extra read of an invalid address under certain circumstances. If it's the address of the status register of an IC that has just received a byte and set the interrupt, and the interrupt is cleared by reading the status register, you can see how someone without a logic analyzer would be tearing their hair out trying to figure out why there's an occasional, unpredictable overrun.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Hi Garth,
Thanks for your reply.
I'm thinking that the bug was something like a status flag didn't get set/cleared with a certain opcode... ???

BTW, my OSI 500 has a 6502 with a 1976 date on it, so I guess it's fairly early.

Speaking of logic analyzers: I just got an HP1615A at the local HAM 'swapfest' - paid $40 for it. When I first started at DEC, I used a 1610 or 1615 occasionally. Back then, they cost $thousands$, I think.

Pete

Someone just gave me an HP1610B logic analyzer along with the manuals. I've never even plugged it in to know if it works, but he assured me it does. I think the only reason it was retired was that it wasn't fast enough for any of the new systems. If someone wants it, you can have it. I live in Whittier, CA. I don't have the shipping box.

One of the NMOS 6502 bugs is that the N, V, & Z flags are invalid after a decimal operation. The bug never existed in the CMOS versions.

Garth

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

The early 6502s [pre June 1976 if I remember correctly] did not have the ROR instruction.

All 6502s up to the 65C02 had a bug with the JMP ($xxFF) instruction. The second byte [high byte] of the address was fetched from the same page [$xx00] instead of the next page [$xx00+$0100] of memory.

Paul R. Santa-Maria
Monroe Michigan USA