more FAS&RTS

[Dmitry V. Volodin]

OK, I've already got several responses on my RTS yell. Some of them
explaining what is RTS, others asking what I've ment. I've posted my
message in order to attract netpeople's attention to VERY common
misinterpretation of RTS. Very typical is to think that RTS controls
the flow from modem to computer (DCE to DTE officially). Here is
a quote from one of letters:

>The serial port standard is asymmetrically named, but is actually
>symmetric.  One of the above is output, and the other is input.
>The signal, output or input, means that "this direction is ready
>to receive another byte".  Serial chips can be programmed so that
>they will respect this input signal and not send until it's ON.
>They also can be programmed so that they receive a byte and drop
>the signal output until you pull that byte out, then they raise
>the output signal and the other end sends another byte.

And here is my reply:

>The above doesn't comply with RS-232 and V.24. RTS is raised by computer
>to indicate the modem (or whatever) that there's some data to send.
>CTS is an indication from the modem that RTS is felt and all the
>procedures to send away data are up and running. This scheme was
>designed primarily for half-duplex modems and has nothing to do with
>stopping the modem (or whatever, forgot that official name) to deliver
>data to computer. The computer is supposed to have fast enough procedures
>to capture data from modems at full speed.
>
>This RTS/CTS misunderstanding is VERY common and, I suspect, appeared
>when smart guys used to wire one computer's RTS to other's CTS to
>make flow control on direct links. What is really painful - other
>smart guys write smart drivers INCOMPATIBLE with canonical ones.
>SCO's interpretation is quite V.24-compliant, and FAS's - just
>clever incompatible hack.

Regards.

Dima

P.S.
Don't think there's no more half-duplex modems in the Unix world -
think about faxes.
-- 
Dmitry V. Volodin <dvv at hq.demos.su>     |
fax:    +7 095 233 5016                 |      Call me Dima (D-'ee-...)
phone:  +7 095 231 2129                 |