Looking for some HOLTEK DTMF dialler chips.

I can't offer you a source but I can offer you a alternative method that may work, at least it did for me to replace a chip in a radio for a automatic keyer.

I found a family of PIC chip that was pin for pin compatible with the original chip as far as the rail legs and IO were concerned. Who knows, maybe that is what it was in the first place? But I was able to program that chip to produce the exact results of the original with a little enhancement to it..

You may want to look that way if your search for replacements come to a dead end.

Jamie

Which PIC has the VSS/VDD on pins 9/10 of an 18-pin dip ??

That won't be necessary. IIRC I once quoted a circuit like that based on a cheap & small MSP430 device. PWM and an RC filter should do the trick.

I'm not familiar with that chip, but generally there is more to a dialer than just producing DTMF. You need to do call progress detection. It varies from country to country, but basically you need to determine if there is a dial tone first. Once you have a dial tone, you blurt out the digits then listen to the line. There still may be a dial tone (i.e. fubar), or you have ring detect or a busy signal.

You could still do it with a PIC, but it is slightly more complicated than you think. But probably not much more complicated. In the dark ages of split band modems, you would take one of the band separation SCFs and change the clock so it overlapped the dial tone frequencies. Using an energy detection circuit, you would decide if a dial tone is present.

I've designed the circuitry in the dark ages for modem CPD, but there are still chips that do just that function. [I can't claim first hand use of these chip. This is just the first valid good hit.]