HD404639R Datasheet, PDF (100/135 Pages) Renesas Technology Corp – 4-Bit Single-Chip Microcomputer

HD404639R Series
DTMF Generator Circuit
The MCU provides a dual-tone multifrequency (DTMF) generator circuit. The DTMF signal consists of
two sine waves to access the switching system.
Figure 81 shows the DTMF keypad and frequencies. Each key enables tones to be generated corresponding
to each frequency. Figure 82 shows a block diagram of the DTMF circuit.
The OSC clock (400 kHz, 800 kHz, 2 MHz, 3.58 MHz, 4 MHz, 7.16 MHz or 8 MHz) is changed into six
clock signals through the division circuit (1/2, 1/5, 1/9, 1/10, 1/18 and 1/20). The DTMF circuit uses one
of the six clock signals, which is selected by system clock select register 1 (SSR1: $029) and system clock
select register 2 (SSR2: $02A) depending on the OSC clock frequency. The DTMF circuit has
transformed programmable dividers, sine wave counters, and control registers.
The DTMF generator circuit is controlled by the following three registers.
1
2
3
A
R1 (697 Hz)
4
5
6
B
R2 (770 Hz)
7
8
9
C
R3 (852 Hz)
*
0
#
D
R4 (941 Hz)
Figure 81 DTMF Keypad and Frequencies
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