17 Jun
2013
17 Jun
'13
12:14 p.m.
I've experienced this, trying to use a USB serial
adapter in place of an
ASR-33 to serve up an imaged paper tape on a PDP-8/e. It does not work.
It's an interesting question as to why this is a problem. :-)
AMny of the trditioal baud rates form a doubling sequence -- 75, 150,
300, 600, 1200, 2400, 4800, 9600, 19200. At onme time lesser serial
interfaces jsut had the appropraite crystal and a binary divider chain
and thus couldn;t do 110 baud. I can remember the fun a friend and I had
trying to get a BBC micro to talk to an ASR33. We had to bit-bang 110
baud...
But surely it doesn;'t take much more logig to implement 110 baud, not
compared to what is needed for USB. SO that probably isn;t the reason.
More likehy they assumed that 'nobody' would want to use 110 baud. Heck,
I've seen devices that won't go slower than 9600 baud.
Another issue with emulating the paper tape reader is that DEC and others
(HP, Intel) added a relay to the ASR 33 to allow the computer to control
the tape. Unless you find soem way of controleldi nthe RS232 interface --
and get it to stop at the end of that chracter, not send a few more
(there is no bufering on the DEC boards) you may well be loosing the odd
character.
-tony