"intelligent" disk drives

Tony Duell ard at p850ug1.demon.co.uk
Fri Nov 16 18:40:25 CST 2007

[CBM disk drives]

> "Controller card" might not be the best term, but yes, there was a
> one board inside with one or more 6502-family microprocessors
> (depending on the drive model).  Older, dual drives tended to have
> a couple of processors (6504s were common) with a few K of shared
> memory; newer drives tended towards one microprocessor (a full 6502
> was common), with a software scheme to simulate the multi-processor
> model of the older drives.
> The older, dual drives also had one analog board for both drive
> mechanisms.  Newer drives had the analog circuitry on the mainboard
> with the processor. 

I've never seen a 2031, but all the GPIB-interfaces double drives contain 
2 processors I think. The 8050/8250 contain a pair of full 6502s, one to 
handle the disk data itself, the other the run the DOS and talk to the 
GPIB port. They communicate via shared memory, IIRC 4K of it (the unit 
uses the well-known trick that a 6502 only drives the address lines when 
the clock input is in one of its states, so by feeding inverse clocks to 
the 2 processors you can easily get them to interleave access to memory).

The control processor ROM is in one of those 6530 RRIOT chips, which 
makes replaicng it a little problematic, although my 8250LP (half-height 
drives, plastic case) has a daughterboard in the 6530 socket containing, 
IIRC, a 6530, the ROM part of which is never addressed and a normal ROM 
chip, along with a very little glue logic.

In all the GPIB dual drives that I've seen, therre is a separate 
'analogue board' containing the motor control circuits, the read/write 
chain, etc.

The serial-interfaced drives used in the C64 processor contain a single 
processor (6502 in all that I've seen) and have all the electronics 
(apart from the spindle motor control) on one PCB.


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