On 2018-05-29 04:00, Clem cole<clemc at 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 at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol