An excellent resource for this and other MPE/HP-UX questions is the SMUG
Pocket Encyclopedia from Robelle.

There is an online version at www.robelle.com/smugbook . Click on "F" and
"flow control" to get a good overview.

The entire pocket encyclopedia is well worth reading.

----- Original Message -----
From: "Peter Smithson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, November 25, 2004 1:32 PM
Subject: Re: [HP3000-L] Serial device FDEVICECONTROL question


> In article <[log in to unmask]>, [log in to unmask]
> says...
>
>> It's UNIX that doesn't transmit the DC1, not telnet. They simply aren't
>> part
>> of UNIX's heritage. The presence of the go-ahead signals that DC1's
>> represent
>> are an MPE-ism not shared by another operating system that I know of.
>
> Perhaps I am misunderstanding it then.
>
> I'm not sure why we are talking about terminals.  This could apply to
> any serial device.  I've seen these DC1's in the terminal output for
> block mode but I'm not sure if that's related.
>
> With UNIX, if a serial device sends too much data then the UNIX device
> driver will send a XOFF or DC1  (ASCII char 17) to tell the device to
> stop sending (as it's buffer is full).  When UNIX is ready to recieve
> again it will send an XON - DC3 (ASCII char 19).
>
> (Thinking about my next paragraph - I may have got those values above
> the wrong way round! Same principle though)
>
> It also works the other way around - from the device.  So if you typed
> "cat filename" on a terminal (to send it to the screen) and wanted to
> stop the output (because the file was very big), you could hit Ctrl-S to
> stop the output and then hit Ctrl-Q to re-start it.  This kind of flow
> control would apply to any serial device.  (you can still do it with
> telnet and TCP/IP but the output is usually too fast these days)
>
> Anyway - that manual page for FDEVICECONTROL sounded a bit like this
> kind of flow control process - I realise from the responses that I might
> be dead wrong.
>
> Thanks.
>
> Peter
> --
> http://www.beluga.freeserve.co.uk
>
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