VT78 - lots of questions

From: ajp166 <ajp166_at_bellatlantic.net>
Date: Sat Dec 30 14:23:47 2000

From: Jeff Hellige <jhellige_at_earthlink.net>


> I believe it was DEC's first microprocessor based PDP-8
>family machine, followed not long after by the DECmate series.


Correct, effectively decmate-I the VT52based version was the first
and second was VT100 based then decmate-II/III.

>Reason for introduction: Using TTL MSI and LSI components, DEC could
> pack a system into the vacant space in a standard terminal
case,
> allowing PDP-8 systems to compete with personal computers in
the
> small business and office automation market. This was a
natural
> follow-on to the desk-mounted workstation configurations in
which
> the PDP-8/A was already being sold.


Actually before 1980 there were very few "personal" computers so the
VT78 was ahead of the pack somewhat.

>Compatability: The Group I OPR combinations RAL RAR and RTL RTR are
> no-ops. Unlike all earlier PDP-8 models, autoindex locations
> 10 to 17 (octal) only work in page zero mode; these operate
like
> all other memory locations when addressed in current page mode
> from code running on page zero. Other than this, it is fully
> PDP-8/E compatable, even at the level of I/O instructions for
> the standard periperals; this was the last PDP-8 to offer this
> level of compatability.


The 6120 chip also had this and improve it a little but they were
actually the
end of the PDP-8 family line!

> the terminal. The console (device 03/04) and the serial ports
> (devices 30/31 and 32/33) are compatible with the M8650 KL8E,
> with the latter extended to allow software controlled baud rate
> selection. There are two parallel ports; device 66 (compatible
> with the M8365 printer controller) and device 47, compatible
with
> the nonstandard port on the M8316 DKC8AA. There is also a
100Hz
> clock compatible with the clock on the M8316 DKC8AA.


This is critical to most programs that would run on discrete PDP-8
systems
would run on the VT78 where the later decmates had a sorta/nearly but not
quite terminal emulation leading to OS/278 varient of OS-8. The
emulation
or existance of KL8e TTY interface at 3/4 was a defining standard for all
PDP-8 software that used a terminal interface.

Allison
Received on Sat Dec 30 2000 - 14:23:47 GMT