11 Mar
2007
11 Mar
'07
5:48 p.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
It doesn't, as-shipped, though I see enough spares in the the schematic
to implement RTS flow control.
The Spare Time
Gizmos SBC6120 (single board pdp8e clone) allows 38,400,
9600, 1200, and 300. There's a permanent mod that adds 110, but I'm put
off by the permanent part. You also lose the 38,400 setting.
Does it support hardware flow control on the console port? If not, then
you're going to have a problem if the machine is seding characters at,
say, 1200 (about 120 cps) baud and your tty is only taking them at 110
baud (about 10 cps, since 110 baud often implies 2 stop bits). You've
got to have a way to tell the faster side to stop sending for a bit. What does the mod consist of? I can't believe
it's really permanent
(although it might well involve soldering to undo it). Losing 38400 buad
is surely not a problem, since few, if any, classic terminals ran at that
speed, and you don't _need_ that sort of data rate for a tectual terminal
anyway.
The baud rate generator is a 4.9152Mhz can oscillator, a 74HC4040
divider, a header and some jumpers. So, the hack is to simply
replace the oscillator with a 1.804Mhz one. I've never seen a
can of that frequency, though, and substituting a 1.8432Mhz
oscillator would leave you about 2% too fast. 3.579Mhz comes
within a percentage point, but you'd need to tap a different
pin on the divider, which would probably involve a blue wire.
(I used sockets for the oscillator cans on mine, so changing
can would be easy for me.)
Vince