What was a Terminal Concentration Device in DEC's products?
cz at alembic.crystel.com
Sun Jan 30 13:43:19 CST 2022
Hm. Looking i see the dj11 had a silo but not dma.
The only thing I can see that did Async DMA was the COMM-IO-P board.
That was a product in 1980 timeframe, based on the KMC11 processor. With
six DZ11's you have 48 serial ports in a 9 board configuration.
Now for trying to unravel what the hell a DMX11 was...
The 9 board concept for 48 ports matches what I see in the Sha Tin
documentation from mid 1977. Apparently the DMX11 was developed by DEC
in 1975-1976 and was a product certified for block mode devices, but the
first version delivered in early 1976 was literally a breadboarded monster.
In the notes it says that DEC originally expected the DMX11 to provide
block mode only (to the cashier and ticket printing machines which
operated in block mode) but signed a contract addendum saying that the
DMX microcode would be upgraded to support block and async mode on the
same controller so they could support VT52's for interactive
applications as well. Apparently this would make the DMX a better
product to sell into other environments and would be a "simple upgrade".
Turns out it was not. And this became a CSS Australia disaster that sank
the whole race track.
Constant hardware and software patches were delivered as DEC tried to
fit the increased microcode on a single board as the HK Jockey Club held
insanely firmly to the contract requirement that the 48 port serial
interface fit in a 9 board layout. Given that they couldn't change the
DZ11's, they tried to mush down the logic in the DMX11 control board and
that plus the change requirement to make it handle block mode devices
and interactive devices doomed the whole project.
From what I can see, the the kmc11 was an M8204 single board which is
different from the 8200 used in the dmc11. I had a DMC11 somewhere.
From the books, the kmc11 had an "lsi11 on board", 1k of 16 bit ram, 1k
of 8 bit data memory a 300ns cycle time, 16 bit microprossor with a 16
bit micro-instruction bus and 8 bit data path. This is according to the
1980 Terminal and Communications handbook, so it's a few years after the
1976 timeframe of Sha Tin.
Now the original LSI11 processor was 4 main chips, an EIS/FIS chip (or
the CIS lite chip or the weird 1k*20 bit micro-ram board which I have
somewhere). The DCT11 was a single chip lsi11 that had an 8 or 16 bit
outside bus and a 16 bit internal structure and ran pdp11 instructions.
So the KMC11 probably had the DCT11 chip.
The LSI11 chipset was around in 1975, so it makes sense that DEC could
use it. The SBC11/21 came out in 1981 but the chip was probably avail
internally by 1980 so I'm guessing that the KMC11 and the COMM-IO-DP was
using the DCT11.
But Sha Tin was 1975-1976. Perhaps the DMX11 was an early concept
version of a KMC11 that had the original LSI11 chip set of 4 chips
running the show with a set of six DZ11's and a smaller amount of
memory. But there wasn't enough space for additional memory to handle
the extra features and DEC got stuck. Maybe part of that mushing work
led to the LSI11 being fewer chips (the PDT11 has only 4 chips but
EIS/FIS thanks to one of the chips being a dual carrier of MicroRoms)
and ultimately to the DCT11.
One item that could really help would be RSX11D version notes. According
to the documentation the DMX11 was supported in RSX11/D but support was
dropped in 1976. They switched to RSX11/M where it was still supported.
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