Back in the day, I worked for Tymshare, a time sharing company
(AKA early cloud computing). We used Bell 103 protocol modems to
provide full duplex connections for our users who were using
ASCII terminals, both CRT and teleprinter. They could type at
the same time the computer was sending data, so the modem was
supporting full duplex.
I note the Wikipedia article
<https://en.wikipedia.org/wiki/Bell_103_modem> mentions:
"The Bell 103 modem used audio frequency-shift keying to
encode data. Different pairs of audio
frequencies were used by each station:
The originating station used a mark tone of 1,270 Hz and a
space tone of 1,070 Hz.
The answering station used a mark tone of 2,225 Hz and a
space tone of 2,025 Hz."
So the modem can both send and receive at the same time if the
communication link supports it.
Other terminals, such as the IBM 2741, could only handle data in
one direction and needed the RTS/CTS lines to support their needs.
And, radio applications would need separate transmit frequencies
and good filtering to support full duplex.
73 Bill AE6JV
On 7/9/18 at 8:07 AM, fc...@montana.edu (Cady, Fred) wrote:
The Bell 103 could send data only in one direction at a time so
RTS and CTS were included to control the flow of the data.
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Bill Frantz | Re: Computer reliability, performance, and security:
408-356-8506 | The guy who *is* wearing a parachute is
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www.pwpconsult.com | first to reach the ground. - Terence Kelly
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