TNIX (Micropolis 1203 and "Board Bucket" systems)

[Tony Duell]

> 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