HD404654 Datasheet, PDF (84/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
DTMF Output: The sine waves of the row-group and column-group are individually converted in the D/A
conversion circuit which provides a high-precision ladder resistance. The DTMF output pins (TONER,
TONEC) transmit the sine waves of the row-group and column-group, respectively. Figure 69 shows the
tone output equivalent circuit. Figure 70 shows the output waveform. One cycle of this wave consists of
32 slots. Therefore, the output waveform is stable with little distortion. Table 26 lists the frequency
deviation of the MCU from standard DTMF signals.
Table 26 Frequency Deviation of the MCU from Standard DTMF
fosc = 400 kHz, 800 kHz, 2 MHz, 4 MHz fosc = 3.58 MHz
Standard MCU (Hz)
DTMF (Hz)
Deviation from
Standard (%)
MCU (Hz)
Deviation from
Standard (%)
R1 697
694.44
–0.37
690.58
–0.92
R2 770
769.23
–0.10
764.96
–0.65
R3 852
851.06
–0.11
846.33
–0.67
R4 941
938.97
–0.22
933.75
–0.77
C1 1,209
1,212.12
0.26
1,205.39
–0.30
C2 1,336
1,333.33
–0.20
1,325.92
–0.75
C3 1,477
1,481.48
0.30
1,473.25
–0.25
C4 1,633
1,639.34
0.39
1,630.23
–0.17
Notes: This frequency deviation value does not include the frequency deviation due to the oscillator
element. Also note that in this case the ratio of the high level and low level widths in the oscillator
waveform due to the oscillator element will be 50%:50%.
VT_ref
GND
Switch control
TONER
TONEC
Figure 69 Tone Output Equivalent Circuit
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