SocketModem question

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I have a V92 SocketModem connected to an AVR M128 uC. When I send commands
to the modem it seems that regardless of the state of the RTS line, the
modem sends its response back to the uC. Unfortunately at any decent serial
speed, I get corrupted bytes back. Does the flow control not apply to
commands or am I missing something more obvious? Any comments welcome.

TIA.

Roger.



Re: SocketModem question
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Interesting problem.

Maybe a dumb question, but... are you sure you have hardware flow
control turned on in the modem?  Does it work otherwise?  (See AT&K3)
http://www.uktsupport.co.uk/reference/modem.htm

Also, a reference in the docs states that RTS/CTS is only supported when
the SocketModem DCE interface is slower than the modem line rate.

Re: SocketModem question

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Thanks for the reply. I'm sure the flow control is active as I've accesses
S39 to check. The SocketModem uses a Conexant chip and since my original
message I've tracked down a datasheet of a similar chip which mentions
something about RTS not being used in command mode. I suspect this is the
simple answer. I would be interested to know the reference that you refer to
in your reply though as I've found the documentation on the SocketModem to
be fairly poor.

Thanks,

Roger.



Re: SocketModem question
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http://www.ssv-embedded.de/ssv/pc104/sktmd1.pdf

Section 2.3 re: Flow Control.  Re-reading it, my interpretation was
backwards - it supports signalling toward the DTE when the line rate is
slower than the port speed.  That makes more sense.

I can see some logic in having command responses bypass the flow
control, since they are typically very small replies and it'd let you
pause the normal data stream and still manipulate the modem.  Still,
you'd think this would be worth a mention in the docs.

Re: SocketModem question
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What's the oscillator on the M128? I have seen problems with using the
internal oscillator because, although it may be nominally 8MHz - say,
the frequency is not quite right so your baud rate is wrong. Some
devices can be alot more sensitive to slight baud rate errors than
others.

Iain

www.claritech.co.uk - Hardware & Software Design

Re: SocketModem question
Yes, my understanding is HW flow control would only be enabled for data
mode.

You might consider putting the modem into "short response mode" (ATV0).
That way it only issues a single char response to most commands.

TOH
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