參數(shù)資料
型號: HD404612TF
廠商: Hitachi,Ltd.
英文描述: 4-Bit Single-Chip Microcomputer
中文描述: 4位單片機
文件頁數(shù): 62/89頁
文件大?。?/td> 358K
代理商: HD404612TF
HD404618 Series
62
DTMF Generation Circuit
The MCU has a dual-tone multifrequency (DTMF) generation circuit.
The DTMF signal consists of two sine waves to access the switching system.
Figure 39 shows the DTMF keypad and frequencies. Pressing a key generates a tone corresponding to its
frequency. Figure 40 shows a block diagram of the DTMF circuit.
The MCU uses an oscillation frequency reduced to 400 kHz, an eighth of the conventionally used
frequency, for low-power consumption. This, however, causes a potential frequency deviation. The MCU
provides transformed programmable dividers in addition to sine wave counters and a control register to
reduce frequency deviation.
The DTMF generation circuit is controlled by the following three registers.
1
4
7
*
2
5
8
0
3
6
9
#
A
B
C
D
R1 (697 Hz)
R2 (770 Hz)
R3 (852 Hz)
R4 (941 Hz)
C
C
C
C
Figure 39 DTMF Keypad and Frequencies
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