HT95LXXX
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
D_PWDN
¾
Bits
R/W
Function
DTMF generator power down
0
RW 1: DTMF generator is at power down mode.
0: DTMF generator is at operation mode.
1
RO
Unused bit, read as ²0²
Tone output enable
TONE
2
RW 1: DTMF signal output is enabled.
0: DTMF signal output is disabled.
DTMFC
(20H)
3
4
5
6
7
RW Reserved, inhibit using.
RW Reserved, inhibit using.
¾
¾
¾
¾
¾
RO
RW Reserved, inhibit using.
RO
Unused bit, read as ²0²
Unused bit, read as ²0²
TC4~TC1 3~0
TR4~TR1 7~4
RW To set high group frequency
RW To set low group frequency
DTMFD
(21H)
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
0
0
0
x
0
1
1
x
0
x
1/2 VDD
1/2 VDD
0
Any valid value
16 dual tones or 8 signal tones, bias with 1/2 VDD
D
_
P
D
W
N
=
1
D
_
P
D
W
N
=
0
1
/
2
V
D
D
T
A
O
N
E
=
1
T
O
N
E
=
0
T
O
N
E
=
0
T
O
N
E
=
0
T
O
N
E
=
1
T
O
N
E
=
1
l
l
t
h
e
t
i
m
i
n
g
o
f
t
h
e
T
O
N
E
=
1
a
n
d
T
O
N
E
=
0
a
r
e
d
e
t
e
r
m
i
n
e
d
b
y
s
o
f
t
w
a
r
e
DTMF Output
Tone frequency
Output Frequency (Hz)
% Error
Specified
697
Actual
699
+0.29%
-0.52%
-0.59%
+0.74%
+0.50%
-0.30%
-0.34%
770
766
852
847
941
948
1209
1336
1477
1215
1332
1472
% Error does not contain the crystal frequency shift
Rev. 1.20
23
May 26, 2004
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
