AVR-Chat

On Sep 29, 2005, at 8:13 PM, Farzlina Ab.Hadi wrote:

> hi everyone!
>
> i am doing a modem communication for a telephony design. we decided  
> to use the v.22bis protocol for modem comm. on my observation, when  
> working at 2400b/s, after handshake , there will be stream of  
> garbage seen on the hyper terminal. so my tx and rx is definitely  
> out. but very clean when doing 1200b/s. tx and rx of data is ok.
>
> may be it is something to do with the telephony board design.it  
> must have created some noise that would interfere the comm at 2400b/ 
> s. because when i test from ext. modem to another ext. modem, it is  
> ok at 2400b/s.
>
> hopefully someone could give some input or ideas. thank you very  
> much for any reply!

About the time of 2400 baud telephone modems there were other tricks  
being performed in attempt to do data compression and network-like  
error detection and correction. "MNP-5" comes to mind. Is possible  
you see extra garbage from an external modem talking to your modem  
when the external is trying to detect extra protocol layers.

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.

It depends on what the modem is "talking to". If it is a
conventional modem, then there may be a series of handshake
steps to establish the correct baud rate. There is more to
the modem protocol than just the bit decoding - the
arbitration, as it is called, is also a big part. You also
need to make sure that the modem at the other end is able
to connect with the protocol you have chosen.

Jim

On Fri, 30 Sep 2005 09:13:19 +0800
 "Farzlina Ab.Hadi" <elin@sapura.po.my> wrote:
> hi everyone!
> 
> i am doing a modem communication for a telephony design.
> we decided to use
> the v.22bis protocol for modem comm. on my observation,
> when working at
> 2400b/s, after handshake , there will be stream of
> garbage seen on the hyper
> terminal. so my tx and rx is definitely out. but very
> clean when doing
> 1200b/s. tx and rx of data is ok. 
> 
> may be it is something to do with the telephony board
> design.it must have
> created some noise that would interfere the comm at
> 2400b/s. because when i
> test from ext. modem to another ext. modem, it is ok at
> 2400b/s. 
> 
> hopefully someone could give some input or ideas. thank
> you very much for
> any reply!
> 
> rgds,
> elin

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