What was a Terminal Concentration Device in DEC's products?

Chris Zach 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.

Weird stuff.

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