HD404618 Datasheet, PDF (66/91 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404618 Series
Table 31 Tone Generator Control Register
TGC
Bit 1
0
1
DTMF Enable Bit
DTMF disabled
DTMF enabled
TGC
Bit 2
0
1
TONER Output Control (row)
Stopped
TONER output (active)
TGC
Bit 3
0
1
TONEC Output Control (column)
Stopped
TONEC output (active)
Tone Generator Speed Flag (TGSP: $020,Bit 2): One-bit register which can be set and reset by the
SEM/REM and SEMD/REMD instructions. The DTMF generation circuit generates output frequencies
with a 400-kHz clock (table 30). With an 800-kHz clock, the DTMF generation circuit generates these
same frequencies by pulling the TGSP flag high.
DTMF Output: The sine waves of the row-group and column-group are individually converted from
digital to analog in the D/A conversion circuit, which provides high-precision ladder resistance. The
DTMF output pins, TONER and TONEC, transmit the sine waves of the row-group and column-group,
respectively. Figure 41 shows thetone output equivalent circuit. Figure 42 shows the output waveform.
One cycle of this wave consists of 32 time slots, making the output waveform stable with little distortion.
Table 32 lists the frequency deviation of the MCU from standard DTMF signals.
VT_ref
GND
Switch control
TONER
TONEC
Figure 41 Tone Output Equivalent Circuit
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