King Billion Electronics Co., Ltd.
HE89C21
駿 億 電 子 股 份 有 限 公 司
HE80000 SERIES
The DTMF generator is controlled through DTMFC (DTMF Control) Register. It is write only, and can
not be to read. The DTMFC register actually maps to Row Register, Column Register and Command
Register. So when writing to DTMFC, the actual register being written is determined by Bit 7 and 6.
DTMFC
ROW HIGH
ROW LOW
COL HIGH
COL LOW
COMMAND
BIT7
BIT6
BIT5
X
BIT4
M10
M4
M10
M4
-
BIT3
M9
BIT2
M8
M2
M8
M2
-
BIT1
M7
BIT0
M6
0
0
0
0
1
0
0
1
1
1
M5
M3
M1
M0
X
M9
M7
M1
M6
M0
M5
M3
HOOK
MUTE
DTMF HB(1)/LB(
0)
Bit 5 of command register (HOOK bit) is the main switch of DTMF Generator block. When HOOK Bit
is ‘1’, the entire block will be turned off and all internal registers will be reset. When HOOK Bit is ‘0’,
the block will be turned on.
The Row and Column registers determine the frequencies of two channels sine wave generator. As they
are 11-bit register, they need to be divided into high parts and low part when writing. The procedure of
changing the Row and Column frequency is by selecting High or Low byte to be written in the command
register, write to the target register, then toggle the HB/LB bit, and then write to the second part of the
register. When both frequencies are set, the DTMF tone can be sent to DTMFO output by turning on bit 1
(DTMF bit) of command register. When DTMF bit is ‘1’, DTMF signal can be output, and the output is
disabled when DTMF bit is ‘0’.
In addition to DTMF generation function, this function block also provides others features which are
useful for the phone application. For example, MUTE bit (bit 3) of command register directly controls
the state of output pin MUTE. When MUTE bit is ‘1’, the state is MUTE pin is set to high impedance ‘Z’,
while MUTE bit is ‘0’, the state of MUTE pin is ‘0’. This pin is useful for muting the microphone of
telephone speech network to prevent speech signal from interfering the DTMF dialing signal when it is
been generated.
15. Absolute Maximum Rating
Item
Supply Voltage
Sym.
Rating
Condition
Vdd
-0.5V ~ 8V
Input Voltage
Output Voltage
Vin -0.5V ~ Vdd+0.5V
Vo
Top
Tst
-0.5V ~ Vdd+0.5V
Operating Temperature
Storage Temperature
00C ~ 700C
-500C ~ 1000C
January 20, 2003
14
V1.0E
KB [ King blillion Electronics Co.,Ltd. ]
