30 May
2018
30 May
'18
4:45 a.m.
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
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