rts/cts - a tutorial on flow control

[Henry Spencer]

> > ...  (What *were* CTS and RTS meant for, you
> > ask?  For turning around half-duplex modems.)
> 
> Halfway correct.  CTS/RTS has slightly different meanings when operating either
> under half-duplex or full-duplex mode.  To quote from the EIA RS-232-C
> standard...
> 
> 		...
> 		The ON condition together with the ON condition on
> 		interchange circuits RTS, DSR and, where implemented,
> 		DTR, is an indication to the DTE (data terminal equipment)
> 		that signals presented on circuit TD (transmit data)
> 		will be transmitted to the communication channel.
> 
> 		The OFF condition is an indication to the DTE that
> 		it should not transfer data across the interface
> 		on circuit TD."
> 
> That last paragraph has the phrase 'flow-control' written all over
> it...

Unfortunately, taken in conjunction with the preceding paragraph it
doesn't, since said preceding paragraph is quite clear about the role
of CTS -- it tells you whether you are connected to the communication
channel, i.e. whether RTS has succeeded yet.

Whether or not the standard says it out loud, half-duplex line turnaround
is very definitely what CTS and RTS were *intended* for.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry