Corvus Concept

From: Frank McConnell <fmc_at_reanimators.org>
Date: Fri Oct 31 22:34:27 1997

kevan_at_heydon.org wrote:
> Last night I acquired a Corvus Concept CPU box and hard disk unit. Does
> anybody have any information about these? More specifically I am
> missing the monitor and keyboard and have no documentation on the
> specifications of these. They are both 9pin D connectors and that is
> all I know.

Well, I am sitting here looking at a little book with title
      
                      HARDWARE
                   DESCRIPTION

            THE CORVUS CONCEPT

You might think that with a title like that it would have connector
pinouts, but, um, not quite. Well, it does have the pinout for the
bus slots, which are like Apple ][ slots less DMA support.

So what can I find about video?

The display area is supposed to be 560 x 720 dots. The monitor used
by Corvus was a Ball HD series monitor (so says the manual) in a
Corvus-peculiar case (so says me).

It looks like all the timing is derived from a 16.364 MHz clock that
is generated on the memory board. That gets divided by the
"horizontal counter" (74163s at U202 then U203 and U204) to produce a
34.669 KHz clock that is the horizontal scanning frequency. There is
also a "vertical counter" (at U301) to produce a 50 Hz or 60 Hz
vertical sync clock.

"The video shift registers comprise 74S299 U106, U206 and 74ls299
U306..U806 for video data. The data is shifted at 16 MHz in two
pairs of registers. The output of one register is fed directly
into a 74S157 multiplexer U104 which is switched between two inputs
at a 16 MHz rate. The other register feeds a 74S112 flipflop
U103 which delays the data by 30 ms and then feeds it to the multiplexer.
This makes a data rate of 32 MHz."

I'm not much of a hardware guy, but I hope that gives you some clues
for board-tracing and monitor selection.

Note that the system can run the monitor in either landscape or
portrait mode (hence the peculiar case, with slots for the base on two
sides). I think you are supposed to tell it how you've got the
monitor positioned with the VERT/HORIZ switch on the back. That
doesn't change the video timing, it changes how the software draws
into the memory.
 
Now what about the keyboard?

I gather there is a 6551 UART at U310 that receives keycodes, one for
each key-down or key-up. Key-down codes have the most-significant-bit
set; key-up codes have it clear but are otherwise identical to key-down
codes.

...

Some other notes.

Jeff Kaneko wrote that the operating system was "Unix-like". I don't
know, I haven't seen it run much less try to hack on it, but from
reading the manuals I'd say it was more p-System like, except that it
runs 68000 code instead of p-Machine code.

The hard disk(s) could be hooked up over the Omninet (in which case the
disk box was connected to an Omninet-attached disk server box) or via a
hard-disk interface that sat in one of the Concept's expansion slots.
There were also expansion cards to control 8" and 5.25" diskette
drives.

I'm not sure exactly how the VCR-backup stuff works. From reading
another manual (the Disk Drive Installation Guide) it looks like there
is an option for the disk to have a "Mirror" built-in. There are
four DIP switches on the back that need to be set different ways for
different circumstances:

    no Mirror built in => all closed
    Mirror built in, NTSC VCR => all open
    Mirror built in, PAL/SECAM VCR => 1 closed, 2-4 open

...

Well, I hope that helps a bit. Yes, I have one of these. No, I haven't
done anything with it as yet, save haul the CPU, monitor, and keyboard
up to VCF for folks to gawk at.

-Frank McConnell
Received on Fri Oct 31 1997 - 22:34:27 GMT