30 Dec
2000
30 Dec
'00
2:23 p.m.
From: Jeff Hellige <jhellige(a)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