HT95LXXX
Rev. 1.20
23
May 26, 2004
DTMF Generator
The DTMF (Dual Tone Multiple-Frequency) signal generator is implemented in the telephone controller. It can generate
16 dual tones and 8 single tones from the DTMF pin. This generator also supports power down, tone on/off function.
The DTMF generator clock source is 3.58MHz, before using this function, the system operation mode must be at Nor-
mal mode.
The power down mode (D_PWDN=1) will terminate all the DTMF generator function, however, the registers DTMFC
and DTMFD are accessible at this power down mode. The duration of DTMF output should be handled by the software.
DTMFD register value could be changed as desired, the DTMF pin will output the new dual-tone simultaneously.
Register
Label
Bits
R/W
Function
DTMFC
(20H)
D_PWDN
0
RW
DTMF generator power down
1: DTMF generator is at power down mode.
0: DTMF generator is at operation mode.
1
RO
Unused bit, read as 0
TONE
2
RW
Tone output enable
1: DTMF signal output is enabled.
0: DTMF signal output is disabled.
3
RW
Reserved, inhibit using.
4
RW
Reserved, inhibit using.
5
RO
Unused bit, read as 0
6
RW
Reserved, inhibit using.
7
RO
Unused bit, read as 0
DTMFD
(21H)
TC4~TC1
3~0
RW
To set high group frequency
TR4~TR1
7~4
RW
To set low group frequency
Note: Bit3, 4, 6 of DTMFC are reserved, always keep the initial value.
The DTMFpin output is controlled by the combination of the D_PWDN, TONE, TR~TC value.
Control Register Bits
DTMF Pin Output Status
D_PWDN
TONE
TR4~TR1/TC4~TC1
1
x
x
0
0
0
x
1/2 VDD
0
1
0
1/2 VDD
0
1
Any valid value
16 dual tones or 8 signal tones, bias with 1/2 VDD
Tone frequency
Output Frequency (Hz)
% Error
Specified
Actual
697
699
+0.29%
770
766
0.52%
852
847
0.59%
941
948
+0.74%
1209
1215
+0.50%
1336
1332
0.30%
1477
1472
0.34%
% Error does not contain the crystal frequency shift
1 ( " 7
4 G
/ / "
"
" ! "
"
4 G
"
"
4 G $ "
"
" A
"
! %
4 G $
4 G
4 G $
4 G
4 G $
H
.
G $
H
.
G
DTMF Output