[HECnet] DDCMP over asynchronous emulated lines on simh 4.0

[Clem Cole]

On Wed, May 1, 2013 at 10:32 PM, Johnny Billquist <bqt at softjar.se> wrote:
Are you sure about Able? I can't remember seeing any such thing from them.

Quite sure - the "other KO" designed it - Ken O'h*   (I don't remember how to spell is last name).   Ken O'h formed Able after Olsen shut him down with the CalData machine (an 11/45 clone).

The Able 16 port serial product was called the DHDM.   I wish I still had one.   I do still have the doc set for them in the basement, along with his original "Enable" card he built for us UNIX guys - which was a slick take on a cache and bus repeater. +

The DHDM could  definitely  do speeds of 19.2K but I think they could do 38.4K and may be higher, I forget - have to look at the prints ;-)    I put the code into BSD support the higher speeds, base AT&T used the EXT A/B stuff.    I'm pretty sure the original DEC DH maxed at 9600.

I want to say it was at a sumer USENIX conference  the late 1980's (Austin maybe) that a number of us tried to get Ken O'h  to put the DHDM on an ISA bus, but Ken O'h did not think he could make enough money at it (he was used to PDP-11 peripheral pricing, not PC community pricing).   Eventually  others created   the "Rocket Port" board became the RS-232C board for much of the early PC/386 based UNIX systems (I think I do still have one them)..

As Ken O'h once said to a number of us.   DEC's KO taught him a lesson and he was careful to never create a processor again.    DEC shut him down for >>sourcing<< the UNIBUS.   His Caches/Repeaters were as far as he would go from a product stand point.    A few years later, he did manage to splice a 68010 on the the Unibus, but I don't he ever sold it because he was scared of KO.   I want to say he gave them to a few people to play with.    I saw the board when I visited him in ~1984 but never programmed it.   But I think I remember that some of the BTL folks might have had a few.

As for your other  comment about "enough for common use" WRT the modem control lines - actually that was not true for the UNIX community.    DZ was short pinned++ one had enough to sort of support >>dial-in<< (i.e. off-hook/CD  detection   but because if used wanted to run uucp, modems needed to control an autodialers and thus needed to support the whole magilla.    Remember UNIX comes from the TPC (The Phone Company) - so base UNIX  had all the support for AT&T communications equipment.

When modems started to add the autodial "in-band" (the @ command stuff - which was not how the AT&T 212 stuff worked), that gave you dial out - but required XON/XOFF for flow control.    Trying to use an in-band flow technique like XON/XOF  was an  anathema  to an 8 bit protocol.    So the fancy modems like the Telebit et al used an out-band scheme keep from  overflowing   - i.e. the modem control signals of RTS/CTS used s a handshake.

In fact on the very cool things that we got Ken O'h to do on the DHDM, was connect the input (which I think I remember is CTS - I've forgotten) and the USART interrupt through an NAND gate so the processor did not get the final "data sent interrupt" until the downstream device was ready for it.    This made a huge difference on PDP-11s and Vaxen.

Clem

Footnotes:
+  I did the SW support for the "Enable"  when I was at Tek.   Johnny since you have asked me for source, one of my earier  academic papers was:   C.T. Cole, S. Huxley, "A Large Address Space UNIX    for  a PDP 11/40"   that describes it.

++   You'll have to accept this as it or send Dave Cane a note directly if you want verified.    Dave as the head of the 750 project (had been part if the 780 did some 11 stuff before and thus did not realize that all the signals mattered).    When Dave did the first version of the Masscomp machine he stole the modem control signals from the console to create a clock interrupt.    I did not join the project until after was too late to fix that.    What a mess ;-)    But Dave learned, RTS/CTS was very important and did not do that again (at least that I now of).