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Old 25th Jun 2022, 7:24 pm   #25
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 4,594
Default Re: Dead commodore 4040 disc drive

I know the 8050 rather better than the 4040 but they are probably similar.

There are two processors in these units (the 8050 is a pair of 6502s, I thought some of the older units used a cut-down version for the 'drive' processor). One handles the IEEE bus, command decoding, etc. The other handles data encoding/decoding to the disk drive heads.

They communicate via a shared area of RAM (the 8050 is 4K*8 in 2114s). The processor clocks are the inverse of each other, each processor only tries to access memory when the clock is in a particular state so this interleaves accesses vey nicely.

From the mention of '6530' (A ROM/RAM/IO chip) in the fault codes, I suspect it's referring to the drive processor
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