On 9/9/2022 5:39 PM, Warner Losh via cctalk wrote:
On Fri, Sep 9, 2022, 3:24 PM Lee Gleason via
Took some pictures of the MicroVAX CTI card,
and another odd card I
got - an 8086 CTI smartcard. See 'em both at
The 8086 card was likely for DOS or CP/M-86 programs... It likely predates
windows and didn't seem to have graphics parts / output (though I suppose
the latter could be over the bus...)
I have one of the Virtual Microsystems PC-Bridge CTI boards (the
commercial 8086 board).
One of the more interesting things about it is that it has its own video
circuitry. It's built up around an Hitachi HD46505/HD6845 CRT
controller with 16 KiByte of video RAM and a character generator ROM (a
lot like a CGA). The board has one of the "long" ZIF connectors with
the additional 30 pins which carry, among other things, the analog video
signals wired directly to the monitor port. The board superimposes its
own video onto that of the system. The PC-Bridge host software just
clears the screen and turns off the cursor. In some cases the host
software can pop up host video simultaneously with the PC-Bridge video.
I assume the PC-Bridge hardware looks for sync on the "GREEN VIDEO"
signal or, possibly, the driver software uses the host video sync
interrupts to do a kind of software PLL to lock the video sources
together. Somehow the fact that both the system and the PC-Bridge board
simultaneously drive the analog video lines works out.
Another really interesting thing about the PC-Bridge board is that it
has DEC-labelled parts on it. I'm not talking about things like
"proprietary" bus interfaces chips. The DRAM SIMMs (used for the
board's main memory) have the digital logo and a DEC part number on them
(1418744-00). In addition the chips are labelled with the DEC convention
(Exx) and are numbered E1, E2,... starting in the lower right hand
corner, with the first chip of each column being labelled on the board,
just as on DEC boards.
This made me suspect that the PC-Bridge board was actually designed by
DEC, or maybe the design was originated by DEC, and so maybe the board
Lee got on eBay was an earlier version of the PC-Bridge.
But it's clear that isn't the case -- Lee's board has a 60-pin ZIF
connector and no apparent CRT controller chip.
I was never able to get the original Virtual Microsystems software
package for my board, but from a friend I did find a Pro hard drive
image with the PC-Bridge application software installed on it. With
that I was able to regenerate the installation diskettes.
All of this is an incredibly roundabout way of saying: I was going to
offer my reconstituted PC-Bridge installation diskettes, but I really
doubt they'll work. In fact, I really doubt the software to drive Lee's
board is easily obtainable at all, given that his board bears no real
resemblance to the PC-Bridge board which, AFAIK, was the only 8086 CTI
board commercially available.
From what I see in the photograph I'd guess that the board works much
more like the DEC "CP/M" (Z80) board. In that case there's a simple
mailbox register with interrupts wired up on both sides. When using the
CP/M board the host is mostly just a dumb serial terminal with some
side-channel floppy and file access. That's why there's no graphics at
all with the CP/M board.