https://www.pagetable.com/?p=406
The MOS 6502 CPU was introduced in September of 1975, and while the documentation described the three shift/rotate instructions ASL, LSR and ROL, the ROR instruction was missing – the documentation said that ROR would be available in chips starting in June 1976. In fact, the reason for this omission was that the instruction, while being present, didn't behave correctly. Only few 6502s with the defect are in existence, and nobody seemed to have checked what was actually going on in these chips.
Simon C got my KIM-1 working again, which has a 6502 from week 51 of 1975. There are 512 possible inputs to ROR (8 bit A plus 1 bit C; assuming it doesn't have dependencies on other registers), and roughly two bytes of output: the 8 bit result and the processor status (flags) register. We ran the following programs on the KIM-1 – note that we had to split the task into several programs, because the KIM-1 doesn't have enough RAM to hold all results.https://www.pagetable.com/?p=406
http://www.cpushack.com/2020/01/14/barn-find-mos-mcs6502-a-restoration/
In car collecting one of the 'holy grail' experiences is the 'Barn Find' finding and recovering a rare vehicle that has sat untouched, in some barn, or shed for some time. They are often in rough, but original condition and can evoke much excitement. As it turns out CPUs are not so different. I recently purchased a very rough and very old ATARI Arcade board.
The pictures clearly showed it in terrible condition, with lots of oxidation and 'stuff' on it. But it also had a white MOS 6502 processor. These are some of the very first CPUs made by MOS and are rather desirable, as in addition to their use by ATARI, they were used in the very first Apple computer, the Apple 1.
(Score: 1, Interesting) by Anonymous Coward on Thursday January 30 2020, @04:56AM (2 children)
"These are some of the very first CPUs made by MOS and are rather desirable, ..."
When I was cleaning out my grandparents' home, in Connecticut, I found maybe a dozen flat plastic trays of CPUs. I set them aside for later examination, and brought them back to California.
Back in California, I got around to doing that research, and discovered they were 6502s. The chips were white, with gold leads. I suspect it was the gold that attracted my grandfather's attention to them, as he was a jeweler.
I still have them, gathering dust. I'll have to read that article and see if I can get in contact with someone who can put these to better use than I can.
~fscked
(Score: 1, Insightful) by Anonymous Coward on Thursday January 30 2020, @05:50AM
(Score: 5, Interesting) by driverless on Thursday January 30 2020, @11:13AM
For anyone who wants to read the story of the 6502's creation, get a copy of "On the Edge: The Spectacular Rise and Fall of Commodore", which devotes a lot of the first part to the design and creation of the CPU. Even if you're not necessarily a Commodore fan, it's still a worthwhile read.
(Score: 2) by shortscreen on Thursday January 30 2020, @09:00AM (1 child)
; lameness filter is lame
(Score: 2) by dry on Saturday February 01 2020, @06:52AM
Weird assembly, the lesser sign represents zero page? Even the mini-assembler in the Apple II knew the difference between
LDA $07 and LDA $0007.
(Score: 0) by Anonymous Coward on Saturday February 01 2020, @03:32PM
In case some other oldsoys enjoy this type of things https://www.youtube.com/watch?v=LnzuMJLZRdU [youtube.com]