KT3170 Vs. MT8870 DTMF Decoders

Does there exists any differences in the decoding response of KT3170/MT8870 DTMF Decoders ?.
I am using MT8870 and have no capability to detect DTMF tones on on-hook state.
But somewhere (**broken link removed**) I have read about KT3170 is that,
Once a call is established (after hearing ring-back tone) on on-hook, if you dial ‘0’ in DTMF mode
KT3170 can decodes this as 1010 without attending the call.

If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues
and the telephone connected in parallel can be used for normal conversation.

If this is true I can simplify my DTMF project by replacing MT8870 with KT3170. In the case of MT8870 I have
to design complex ring detection circuit to automatically off-hook.


Many peoples obtained positive result by following the circuit in the above link using KT3170.
My phone-set have no caller id facility. Does there any possibility for the caller ID (CLIP) signal to come ?
Which mode is used to send caller information in India (FSK or DTMF). If it is DTMF, I think DTMF Decoders can detect DTMF tones on on-hook state.

You may use M8870 in place of KT3170 and vice versa.
The said circuit was published in EFY magazine and is now modified by Kits n spares to make it work. You may get all the components, with description and all the components with PCB from thier dealers all over India..

Both ICs are identical. DTMF is decoded irrespective of whether the the remote party is off hook. As long as there are tones at the input of dtmf decoder, it will decode irrespective of whether the phone is on hook or off hook. That's how dtmf caller id works in India.

Sunish