rpw3@fortune.UUCP (12/14/83)
#R:oliveb:-23800:fortune:3100001:000:992
fortune!rpw3 Dec 13 22:46:00 1983
Pure speculation, but...
1200 baud full-duplex "async" modems are not really async, since they
use phase-coherent modulation. They are really synchronous modems with
one-bit (or more) elastic buffers (FIFOs) for delaying your async
characters into the synchronous slots. (This also permits them to
accommodate a SMALL amount of difference in baud rate.) The early
VADIC 1200 baud jobs even let you run the modem in true sync, if you
wanted to (at least one stat/mux manufacturer ran the trunk line on them).
My guess is that the modem you refer to uses some kind of SIO/UART/USART
to receive the async for presenting to the modulator (though I have no
idea why one might want to do that). Such chips cannot (directly)
propagate <break> without lots of pain from software diddling the
status bits.
Again, just a guess.
Rob Warnock
UUCP: {sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3
DDD: (415)595-8444
USPS: Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065edler@cmcl2.UUCP (Jan Edler) (12/15/83)
The Bell 212A also allows for running in synchronous mode at 1200 bps. Jan Edler cmcl2!edler (New York University) edler@nyu (212) 460-7314