278
Table 11.3 indicates the frequency deviation between the DTMF signals output by the DTMF
generator and the nominal (standard) signal values.
Table 11.3
Frequency Deviation of DTMF Signals from Nominal Signals
Symbol
Standard Signal
Frequency (Hz)
DTMF Signal
Output (Hz)
Frequency
Deviation (%)
R1
697
694.44
–0.37
R2
770
769.23
–0.10
R3
852
851.06
–0.11
R4
941
938.97
–0.22
C1
1209
1212.12
0.26
C2
1336
1333.33
–0.20
C3
1477
1481.48
0.30
C4
1633
1639.34
0.39
11.3.2
Operation Flow
The procedure for using the DTMF generator is given below.
1. Set the OSC clock division ratio in DTLR to match the frequency of the connected system
clock oscillator (1.2 MHz to 10 MHz in 400-kHz steps).
2. Select a row (R1 to R4) and/or column (C1 to C4) frequency with bits CLF1, CLF0, RWF1,
and RWF0 in DTCR.
3. Select row and/or column output with the CLOE and RWOE bits in DTCR, and set the DTEN
bit to 1 to enable the DTMF generator.
This procedure outputs the selected DTMF signal from the TONED pin.