Hi Narin,

So now we can go ahead. Let's call the data sending end <Master> and the terminal end <Slave>, (though quite not as such but for clarity purpose only).


Slave end:
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Make a ring detector circuit and connect it to micro which is also connected to MT8888.

Set the code to accept x number of rings before going OFF-HOOK (switching the off hook relay on).

After going off-hook start sending a character say (*) at a reasonable rate say 1 Hz.

Master end:
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When the data (temperature) is to be sent, dial the number. Wait for a while as long as x number of rings take, slightly longer delay would be better.

Start reading (*). As soon as the (*) is detected send a character say (#) in acknowledgement.

Slave end:
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After sending each (*) try to read a (#). As soon as (#) is detected stop sending any further (*). Now the link has been established as master has acknowledged.

Now data can be sent enclosed by any set of characters for start of data and end of data. Acknowledgement characters may also be included.

Hope above helps.

Simon