DTMF Decorder & 8870 Chips

I was wondering if anyone had any idea's on how too intergrate a DTMF decorder with a microcontroller.

The application i am using this for is, too have a PIC MCU control a secured enterance on an apartment building and i want the PIC too call through existing phones too each suite. Once the call is received, the tentant can hit the # key too let the user in. I have all the other ends of this project underway, just the intergration of the DTMF circuit is giving me some trouble.

Anyway help would be great.

I've used the Teltone M-8870. As I recall it was very easy. You get 5 output bits, 4 of them with a digital code telling you the button that's pressed, and a 5th that goes high when any button is activated. You just get the processor to monitor this and read the 4-bit code when needed. There's also an output enable line for the 4 identity bits but you can leave this enabled all the time if you want. The chip's oscillator runs off a TV colorburst crystal (3.579545MHz).

DTMF Circuits

I just have a few other quick questions and though maybe you could help me out with them that would be great.

First, that Chip you were talking about the Teltone M-8870, is this a TTL or CMOS IC? if so, how did you handle the high Voltage from the phone lines? Optoisolaters possibly?
Next, you said there was 5 Output Pins on this chip, 4 of which being data, can i use this chip too send Singals aswell?
I will tell you why, for my appliacation, i am not worried about receiving Keytones(Just one Keys at the Most), but i need my system too be albe too dial a Phone number, the user too Answer and then Press a Key and this will come back too the pic which will open a door.
Any details you would have on connecting the phone line too The M-8870 too phone lines or if you know where i can find a datasheet for this chip would be great

Thanks

lee_man_tbu