Hi Armbuster,

Do not confuse. You don't need a SLIC if you are going to make a single unit application and not a complete centralized office network.

I assume you want to make just a dialer.

I also assume you want to receive the rings also.

So lets proceed as follows:

Take a transformer out from a screwed one modem. (or buy a 56k modem and screw it)

Now for ring detection use a line capacitor (330nF/400V) and brige rectifier and current limiting resistor (22K/1Watt). This DC output you give straight to an opto 4N35. The opto will give out put when ring AC voltage / signal is present in the line. Use the output of opto as you wish. One appropriate use is to go off hook after counting the desired number of rings.

Now for off hook, connect one side of the transformer to the line in parallel. Measure the voltage accross the line. It should be equal to the off hook with a normal telephone set in your country. If the voltage drop is too much then connect 2watt resistor in series of the transformer with the line. The common values you may select between 100 ohms to 500 ohms, depends. Now you have a proper off hook.

And don't forget that transformer should connect and disconnect to the line through a relay switched from your micro.

Now DTMF. Connect one leg of the transformer of the other side to the ground of your circuit.

Tie up together the two signals namely DTMF/CP and DTMF OUTPUT on page 4-43 of the data sheet of MT8880.

Connect this tie up to the second leg of the transformer.

So, with the above your hardware layout is complete. You can refine it to suite your needs.

If you have any problem with the software, we can talk.

Don't have any fun, go straight to the work and work harder.

Simon