Epson S1C63558 4.14.4 Tone mode (DTMF)

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Telephone Function)

4.14.4 Tone mode (DTMF)

In tone mode, the dialer outputs a tone (pushbutton dial) signal. This mode is set by default at initial reset. To change the mode from pulse mode to this mode, write "0" to the TPS register (FF10H•D3).

The PB (tone) signal generates two different frequencies that are determined by the pushed button in the push button matrix as shown in Table 4.14.4.1.

Table 4.14.4.1 PB frequency combination

Frequency	COL1	COL2	COL3	COL4
(Hz)	1209	1336	1477	1633
ROW1	1	2	3	Unused
697
ROW2	4	5	6	Unused
770
ROW3	7	8	9	Unused
852
ROW4	∗	0	#	Unused
941

The row and column frequencies and the compound tone signal are generated by the DTMF (Dual Tone Multi-Frequency) generator. Figure 4.14.4.1 shows the block diagram of the DTMF generator.

Data bus

3.58 MHz	Frequency	Row group	Sine-wave	D/A
		programmable	pattern
oscillator	divider			converter
		divider	ROM
				–	TONE
				+
	SINR
Control		Column group	Sine-wave
				D/A
	SINC	programmable	pattern
registers				converter
		divider	ROM
				Vref

Fig. 4.14.4.1 DTMF generator block diagram

As shown in Figure 4.14.4.1, the DTMF generator generates each frequency by dividing the OSC3 (3.58 MHz) clock. Therefore, the OSC3 oscillation circuit must be turned ON before using the DTMF generator (it is not necessary to switch the CPU system clock to OSC3).

Two frequency dividers are provided for the row group and column group. The actual generated frequencies are listed in Table 4.14.4.2. They may include an error within tolerance due to the dividing method.

Table 4.14.4.2 Standard vs actual frequency

ROW/COL	Tone output frequency (Hz)		Error (%) *
	Standard	Actual
ROW1	697	701.32	+0.62
ROW2	770	771.45	+0.19
ROW3	852	857.17	+0.61
ROW4	941	935.10	–0.63
COL1	1209	1215.88	+0.57
COL2	1336	1331.68	–0.32
COL3	1477	1471.85	–0.35
COL4	1633	1645.01	+0.74

∗Errors (%) do not include oscillator drift.

116 EPSON S1C63558 TECHNICAL MANUAL