HD404669 Datasheet, PDF (91/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 Series
DTMF Generation Circuit
The MCU provides a dual-tone multifrequency (DTMF) generation circuit. Figure 69 shows a block
diagram of the DTMF circuit. A DTMF signal consists of two sine waves corresponding to the numbers
and symbols on a telephone keypad. DTMF signals are used to access telephone switching equipment.
Figure 70 shows the DTMF frequency matrix.
The OSC clock (400 kHz, 800 kHz, 2 MHz, 3.58 MHz, 4 MHz, 7.16 MHz, or 8 MHz) is changed into
seven 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 seven clock signals, which is selected by the system clock select register 1, 2 (SSR1: $029,
SSR2: $02A) depending on the OSC clock frequency. The DTMF circuit has transformed programmable
dividers, sine wave counters, and control registers.
The DTMF generation circuit is controlled by the following three registers.
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