>> I'm all for making pics do as much as possible, but you'll have a tough
>> time making a cost-effective replacement for a <$2 part like this.
>
>
>I can dedicate a senior engineer to solving this problem for a year if it
>lowers
>the parts cost of my product by $1. The trick of course is weighing the
> difference
>between buying a beefier PIC to solve the problem versus using the dedicated
>chip.
>
>I was talking to a telecom guy about this problem and he claims that 90% of
>the signaling gear he encounters, generates the DTMF with a syntesizer chip.
> This
>means that the two tones are essentially equal in amplitude and their phase
>relationship is constant. You can't design telco gear assuming this, but you
>also can't design RS-232 interfaces with just a diode :-)

   I missed the start of this - I assume by "beefier PIC" the poster meant
"a PIC with D->A capability or higher processing power."

   How about using PWM output with a single digital pin and a PWM->analog
conversion (just an integrator or maybe just a cap?). The PWM
representation of DTMF might be simple enough to express as a formula
rather than a monster table (thus some quickly executing code, and possibly
pretty compact code at that). I guess it would really depend on just how
pure those sine tones need to be, that would drive how intricate the
code/table would need to be, how many interrupts each second to yield the
needed PWM timing resolution etc etc.