17 Nov
2007
17 Nov
'07
12:40 a.m.
[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.
-tony