DECMate III

From: Roger Ivie <IVIE_at_cc.usu.edu>
Date: Tue Feb 16 11:23:40 1999

> On Tue, 16 Feb 1999, Roger Ivie wrote:
> >No. 15-pin cable provides video and power for the monitor as well as a
> >serial port for the keyboard; although it looks like a VT220, it's a
> >monitor and a keyboard, not a terminal.
>
> Is there a way to log into the D-25 COMM port?

That depends on what you mean by "log into" and how determined you are.

One of the operating systems available on the DECmate was CTOS, allegedly
some sort of multiuser commercial operating system. I've not used it, so
I can only spread rumors about it. It might be possible to "log into" a
CTOS system from the comm port.

As far as OS/278 and WPS goes, the video/keyboard is the console. The
console is run via a combination of hardware and slushware; the slushware
provides terminal emulation services and the hardware provides the hooks
needed by the terminal emulation services to appear as a normal console
type serial device to OS/278 and WPS (which expect to talk directly to
the console UART rather than via some sort of device driver).

If you are sufficiently technically equipped and inclined, it should be
possible to switch the console port (on which the emulator runs) and
the 9-pin serial port for the printer. The first thing done by the
firmware (before it checksums the ROM and loads the slushware) is to
program the I/O addresses of the various hardware ports. It is possible
to switch a few instructions in the initialization sequence to swap the
addresses of the printer and console ports. Although I've _thought_ about
doing this and investigated far enough to determine that it ought to work,
I've not actually _tried_ it, so I could be wrong.

There are a number of fun bits involved. The PDP-8 is a 12-bit machine.
The ROMs are 8-bit parts (2716s). There are three ROMs, providing a
4Kx12 memory image for the PDP-8. The ROMs are interleaved in a funny
way; I figured it out once and Lasner was able to use the information to
extract a ROM image and disassemble it, but that was a few years ago. I'd
have to figure it out again.

Roger Ivie
ivie_at_cc.usu.edu
Received on Tue Feb 16 1999 - 11:23:40 GMT