Description

The DTMF (Dual Tone Multiple Frequency) application is associated with digital telephony, and provides two selected output frequencies (one high band, one low band) for a duration of 100 ms. A benchmark subroutine has been written for the COP820C/840C microcontrollers, and is outlined in detail in this application note. This DTMF subroutine takes 110 bytes of COP820C/840C code, consisting of 78 bytes of program code and 32 bytes of ROM table. The timings in this DTMF subroutine are based on a 20 MHz COP820C/840C clock, giving an instruction cycle time of 1 ms.