Michael,

On Tue, 2 May 2006 13:12:40 +0100, Michael Rigby-Jones wrote:

> 
> 
> >-----Original Message-----
> >From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
> >Sent: 02 May 2006 13:04
> >To: Microcontroller discussion list - Public.
> >Subject: Re: [EE] Looking for single channel RS232 @2.5V
> >
> >
> >>rs232 isn't spec'ed for 500m of cable.  IIRC, it has specs like:
> >>1) maximum speed 19200
> >>2) 19200 has a cable length limit of about 20 feet.
> >>3) "HW flow control" doesn't exist.
> >
> >I guess RTS control of a multidrop modem isn't flow control? 
> >CTS says the link is ready to accept.
> 
> RTS/CTS is generaly controlled by software rather than the UART though, so not HW flow control?

Errr - no!  It doesn't work like that.  It's nothing to do with where the decision is made, but how the 
signals travel between sender and receiver.

HW flow control uses RTS/CTS signals on separate channels (wires) from the data (sometimes called "out of band 
signalling").
SW flow control sends XON / XOFF characters in the normal data channels to start and stop the data flow ("in 
band signalling").

Cheers,


Howard Winter
St.Albans, England


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