3 May
2007
3 May
'07
3:20 p.m.
There was a "blank" prototyping board
available for these systems. I
did build an interface board for a Micropolis 1203, so I could use a
hard disk on the "FLEX" 6809-based operating system. It was a pretty
trivial parallel interface, with, IIRC, a line that controlled reading
or writing from the onboard controller, and a "data or status/command"
signal that told the controller where you are tell the controller
whather you are reading or writing control commands, or data.
It was an 8-bit data interface, parallel, with a strobe signal to
read/write data to/from the controller. There were a couple of status
There are 2 possible interfaces for the Micropolis 1203.
The dare drive has a 50 pin connector, which is somewhat similar in
concept to the SMD interface. There's an 8 bit parallel data bus with
strobe lines, etc, to do things like head postiioning, and a raw data
stream.
There was a Micropolis controller board, the same physical size as the
drive logic board, that could be scrrwed onto the drive. I think the host
connector on that was also 50 pin, and it has the interface you're
describing. This controller did the conversion between the 8-bit parallel
data to the host and the bitstream to the drive.
The Tektronix machine that startyed this thread used that controller (so
presuanly it was also common on drives obtained from Tektronix surplus).
The PERQ 2T1 (the onterh machine I have which uses this drive) doesn't.
It has an ICL-designed 'DIB' (Disk Interface Board) that does the clock
recoverry and MFM encoding/decodeing , and makes the host interface similar,
but not idetocal to that on the SA4000 (14" WInchester) so that it could
link to a PERQ I/O board
Other than these drives being rather noisy, and
requiring quite a bit of
power, they were rock solid reliable, and very easy to interface to.
I've had to fix a couple of electronic faults on them, particuarly in the
head psitiuoner analogue section. The positioner coil drive amplifier is
an LM379 (a number forever eteched in my brain), which was desigend as an
stereo audio power amplifier. Here it's used a a full-bridge driver in
the obvious way. The LM379 has the interesting feature that the bottom
end of the output stage for each half of the chip is brought out to a
separate pin on the package, and the Micropolis 1203 connects a low value
resistor between that pin and gorund so as to be able to measure the
positioner coil current (this is one of the feedback terms in the servo
system). So most other stereo power amp ICs won't replace it.
And the LM379 is very hard to find now. It was used as the deflection
amplifier in the Vectrex, and I think other vector-based video games, but
that's hardly a suitable source for spares.
That chip failed in my PERQ's drive, and I was quoted well over \pounds
100.00 for an (untested!) replacement. AI then raided my junk box and
found _one_ spare, which got my PERQ booting again, but what I do next
time it failes I don't know. Probably design a replacement using a pair
of mono audio amplifier chips.
One one edge of the drive logic PCB there's a 34 pin header. THis is for
a text box. I designed a version of that (it's pretty simple, a few
toggle swtiches,, a few LEDs, and a couple of TTL chips). If the drive's
microcotnrolelr detects a fault, said test box will display the error
code. Of course you then need the appropraite pages of the service manaul
to look up said code.
-tony