HD404618TF datasheet(64/91 Pages) RENESAS

Part #	HD404618TF

Description	4-Bit Single-Chip Microcomputer

PDF	91 Pages

Scroll/Zoom	100%

Manufacturer	RENESAS [Renesas Technology Corp]

Direct Link	http://www.renesas.com

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64 / 91 page

HD404618 Series

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.

R1 (697 Hz)

R2 (770 Hz)

R3 (852 Hz)

R4 (941 Hz)

Figure 39 DTMF Keypad and Frequencies

HD404618TF Datasheet(PDF) 64 Page - Renesas Technology Corp