I agree with Per that using three DTMF decoders to try to detect codes in sequence is a strange solution. Why spend money on redudant hardware when you have an MCU that can easily detect sequences of tone_pairs with no problem. I would use an interrupt triggered off the "Data Valid" signal so that the MCU can capture the detected code and then re-arm to get the next code.

I see additional problems with a string of decoders in that as the first one gets done detecting the first code how can you be sure that the 2nd one may be seeing the ending of the first tone instead of the subsequent second tone packet???

With one decoder,if you manage the interface of the part with a timer interrupt, you could even close a detect window after one tone before you enable for the next tone. This forced gap may reduce your false detects by a fair amount.

Michael Karas