On Feb 9, 2007, at 7:34 PM, Vitaliy wrote:

>  I don't know what, specifically, the "half-duplex things"
> are, in Willaim Chops Westfield's post.
>
I didn't explain it either.  In real rs232, you use things like
RING, DSR, DCD, and DTR to do modem, terminal, and call setup,
and don't play a part during the "normal" part of the connection.
When the terminal is ready to transmit data, it asserts RTS (ready
to send.)  the modem use this to enable its transmitter, whatever
that may include, and asserts CTS (clear to send) in response,
which tells the terminal that it may begin to transmit data (this
last part is what leads to the "flow control" interpretation.  The
"bending" of the CTS specification is less than the bending of RTS.)
When the terminal is done transmitting, it drops RTS, the modem
moves itself back into receive only mode and drops CTS so that
the terminal knows it can now expect to be receiving data.
Hopefully some other protocol ensures that the other end of the link
is in the opposite state; I think this can happen either via higher
level protocols within the transmitted data (bisync?), or lower level
protocols directly between the modems.

BillW
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