26 Jan
2014
26 Jan
'14
9:14 a.m.
On Tue, Jan 21, 2014 at 09:53:56PM -0500, Ethan Dicks wrote:
[...]
In general, split baud rates were to allow higher
transmit speeds from what a
CPU could handle in the way of receive speeds, often because of interrupt
handler latency. It was semi-common in machines in the 1970s that had to
support multiple serial-attached peripherals, like time-sharing systems with
many simultaneous user terminals.
Another reason for split baud rates is for modems that wish to allocate more of
the scarce shared bandwidth to one direction. For services such as Prestel that
mainly sent 1kB "frames" of information and expected single-character typed
replies, 1200/75 was much more responsive than the other option of 300/300.
ADSL is a good contemporary example of this, although the implementation is so
unlike serial transmission that "baud" isn't a useful measure. (It's
4,000 baud
in both directions.)