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CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Telephone Function)
4.14.4 Tone mode (DTMF)
In tone mode, the dialer outputs a tone (pushbutton dial) signal. This mode is set by default at initial
reset. To change the mode from pulse mode to this mode, write "0" to the TPS register (FF10H•D3).
The PB (tone) signal generates two different frequencies that are determined by the pushed button in the
push button matrix as shown in Table 4.14.4.1.
The row and column frequencies and the compound tone signal are generated by the DTMF (Dual Tone
Multi-Frequency) generator. Figure 4.14.4.1 shows the block diagram of the DTMF generator.
3.58 MHz
oscillator
Control
registers
As shown in Figure 4.14.4.1, the DTMF generator generates each frequency by dividing the OSC3 (3.58
MHz) clock. Therefore, the OSC3 oscillation circuit must be turned ON before using the DTMF generator
(it is not necessary to switch the CPU system clock to OSC3).
Two frequency dividers are provided for the row group and column group. The actual generated frequen-
cies are listed in Table 4.14.4.2. They may include an error within tolerance due to the dividing method.
116
Table 4.14.4.1 PB frequency combination
Frequency
COL1
(Hz)
1209
ROW1
1
697
ROW2
4
770
ROW3
7
852
ROW4
941
Row group
Frequency
programmable
divider
divider
SINR
Column group
programmable
SINC
divider
Fig. 4.14.4.1 DTMF generator block diagram
Table 4.14.4.2 Standard vs actual frequency
Tone output frequency (Hz)
ROW/COL
Standard
ROW1
697
ROW2
770
ROW3
852
ROW4
941
COL1
1209
COL2
1336
COL3
1477
COL4
1633
Errors (%) do not include oscillator drift.
COL2
COL3
COL4
1336
1477
1633
2
3
Unused
5
6
Unused
8
9
Unused
0
#
Unused
Sine-wave
pattern
ROM
Sine-wave
pattern
ROM
Error (%) *
Actual
701.32
+0.62
771.45
+0.19
857.17
+0.61
935.10
–0.63
1215.88
+0.57
1331.68
–0.32
1471.85
–0.35
1645.01
+0.74
EPSON
D/A
converter
–
+
D/A
converter
Vref
S1C63558 TECHNICAL MANUAL
TONE
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