HD404669 Datasheet, PDF (96/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 Series
DTMF Output: The sine waves of the row-group and column-group are output from the DTMF output
pins (TONER and TONEC). These are output by a high-precision resistance-ladder type D/A converter.
Figure 74 shows the TONE output pin equivalent circuit, and figure 75 shows the output waveform. One
output waveform cycle is composed of 32 slots, giving stable output with a low distortion factor. Table 21
shows the deviation of the output frequencies with respect to the standard DTMF signals.
Table 21 Frequency Deviation of the MCU from Standard DTMF
(f_OSC=400kHz, 800kHz, 2MHz, 4MHz, 8MHz )
Standard DTMF (Hz)
MCU (Hz)
R1
697
694.44
R2
770
769.23
R3
852
851.06
R4
941
938.97
C1
1,209
1,212.12
C2
1,336
1,333.33
C3
1,477
1,481.48
C4
1,633
1,639.34
Deviation from Standard (%)
–0.37
–0.10
–0.11
–0.22
0.26
–0.20
0.30
0.39
Table 22 Frequency Deviation of the MCU from Standard DTMF (f_OSC=3.58kHz, 7.16MHz )
Standard DTMF (Hz)
MCU (Hz)
Deviation from Standard (%)
R1
697
690.58
–0.92
R2
770
764.96
–0.65
R3
852
846.33
–0.67
R4
941
933.75
–0.77
C1
1,209
1,205.39
–0.30
C2
1,336
1,325.92
–0.75
C3
1,477
1,473.25
–0.25
C4
1,633
1,630.23
–0.17
Notes: 1. The DTMF signal frequency deviation must be within ±1.5%, totaling the values in tables 21 and
22 and the precision of the oscillator used. When an f_OSC frequency of 3.58 MHz or 7.16 MHz is
used, in particular, the frequency deviation is greater (max - 0.92%) than with an f_OSC frequency
of 400 kHz, 800 kHz, 2 MHz, 4 MHz, or 8 MHz, and thorough consultation with the oscillator
manufacturer is essential before deciding on the oscillator to be used.
2. This frequency deviation does not include the frequency deviation of the oscillator. Also, the
ratio of oscillator waveform high-level width and low-level width in this case is 50% : 50%.
96