MT8880C DTMF transceiver with 9S12C128

[ve3id]

I am trying to use the MT8880C DTMF transceiver in a ham radio repeater controller, using the 9S12C128 chip, and programming it with gcc.

I have it working fine for output setting it up by the instructions in the data sheet. As part of a POST, I send all the DTMF digits in non-burst mode OK.

Again, following the guide in the data sheet, when I add the code to read the data register when I get an IRQ from valid DTMF, it subsequently starts sending constant tone even though I don;t tell it to, and forever hold the IRQ line down LO.@

I am hoping someone has been there before and can shine some light on the problem!

thanks for any help,

Nigel ve3id

[iggi]

Hi,

i don't see any functional problem of S12C MCU from your description. Are you saying that there is a problem with IRQ pin?

Carl is right. A status register should be read in order to clear the flag. But in case of XIRQ and IRQ interrupts, there is no status register.

Regards,

Ivan

[mculater]

Used this chip years ago in a payphone application, Nigel--  and I seem to recall the IRQ pin has an alternate function as Call Progress detection, related to the on-chip op amp.  Have a look at the data sheet and make sure you have the correct mode selected and the op amp pins conditioned appropriately.  Or you may have to read the status register to clear the interrupt...

Hope that gives you some clues...

Carl :smileyhappy:

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Carl Barnes

www.technologicalarts.com

Modular 9S12 boards for OEM and training.