I use an at89s8252 uC.

To control DTMF timing i use timer 2 (89s8252 has 3 timers).

MT8888 is in non-burst mode, and continuos tone generation:

CRA=0x09;//tout =on;rsel = b;
CRB=0x01;//non-burst mode;
digit = _number to dial_;
wait(100);//wait 100ms;
CRA=0x0C;//tout =off;irq = on;rsel = b;
CRB=0x00;//burst mode;
wait(100); wait 100ms;
CRA=0x09;//tout =on;rsel = b;
CRB=0x01;//non-burst mode;
digit = _next number to dial_;
CRA=0x0C;//tout =off;irq = on;rsel = b;
CRB=0x00;//burst mode;
//end;

I wish it could help U.
[]'s
Evandro Zilio de Souza