30 May
2018
30 May
'18
6:19 a.m.
A few comments.
1). If you grab ^s/^q from the alphabet it means you can send raw 8 bit data because they
are valid characters (yes you can use escape chars but it gets very bad)
2) RTS/CTS flow signaling was very much part of the standard but it’s optional and was
used differently by the bell modem interface spec as you point out. I have the spec full
somewhere. It was originally in the ECMA standard for RJE stations actually. IIRC it was
the one if the European firms like ICL that created it. Again IIRC MacNamera describes it
also in his early19079s classic book on data com.
3) DEC did not stick to the standard on the DZ11 neither ECMA interface nor the WE/Bell
system standards. either Paul is absolutely right. It drove MacNamera crazy as I believe
he was the lead designer of the original DH which did (the topic came up at a party once).
WE212 modems worked on dz11 for input but just barely and could not use a WE dialer for
output (who’s number I now forget). Remember the AT command dialer stuff was not
originally a standard from the telcos. The modems were independent of the dialer (which
used the RS-4xx standard and I also have some where and I forget the number).
15 WE212 Modems went into WE modem rack and the first slot was special and could support
either a 16tg modem or a single WE dialer which was common the 15 modems in the rack.
The logic to make it all work is well described and spelled out in the original UUCP
code.
Btw Tom Truscott of UNC I believe built a home made dialer that snapped a relay over the
pots line to simulate a dialer using a DR11C and did paper in the 1980 winter usenix in
Boulder (aka the black hole) — at the time the AT modem stuff did not yet exist, but
universities often did not use the WE standard modems of racks (Racal Vadic was popular)
and the original dec dialer interface to the bell system stuff I think I remember was from
DEC’s CSS group and not easy to get.
Sent from my PDP-7 Running UNIX V0 expect things to be almost but not quite.
On May 29, 2018, at 6:45 PM, Johnny Billquist
<bqt(a)update.uu.se> wrote:
On 2018-05-29 04:00, Clem
cole<clemc(a)ccc.com> wrote:
And the other issue was besides not enough buffering DZ11s and the TU58 assumes software
(^S/^Q) for the flow control (DH11s with the DM11 option has hardware (RTS/CTS) to control
the I/O rate. So this of course made 8bit data diificult too. And as Paul points out,
with HW flow the priority could have been lower. But the HW folks assumed a so called 3
wire interface because they thought they were saving money.
Uh? Say what? What does XON/XOFF flow control have to do with 8bit data?
And no, DEC was not trying to save money. They were actually sticking to the standard.
Something very few companies managed to do, especially when it came to the RS-232
standard.
The "hardware flow control" is actually an abuse of the half duplex
signalling.
And it does not necessarily work as you might expect if modems are in the middle.
You could get by with just three wires on serial ports, but DEC usually did want people
to have more wires connected, in order to detect when a device was connected or not. But
no, they did not abuse the half duplex control to do hardware flow control. The DZ11 also
have partial modem control. You cannot run them in half-duplex mode, and they do not
support the secondary channel stuff, but they do support more than just the 3 wires.
A few years later when people tried to put high
speed modems like the Trailblazers on them, let’s say the Unix folks quickly abandoned any
hope. Ken O’Humundro at Able Computer has quite a business in his ‘DHDM’ board that was
cheaper than the DZ, more ports, full DMA and of course full hardware flow control.
Yes. It's essentially a DH11 with a partial DM11 on just one board, while the
original DH11/DM11 was a fully 9-slot backplane. So it was a really good alternative. The
DH11 is much better than the DZ11, but did in fact cost more. The Able board gave the DH11
capabilities at a much lower cost, and taking much less space in the box. And it actually
performed better than the DH11. But it did not support the full functionality of the DM11.
But what was lacking was the half duplex stuff, which noone really cared about anymore
anyway.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt(a)softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol