King Billion Electronics Co., Ltd.

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HE89C21

HE80000 SERIES

January 20, 2003

14

V1.0E

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

BIT7

BIT6

BIT5

BIT4

BIT3

BIT2

BIT1

BIT0

ROW HIGH

0

0

X

M10

M9

M8

M7

M6

ROW LOW

0

0

M5

M4

M3

M2

M1

M0

COL HIGH

0

1

X

M10

M9

M8

M7

M6

COL LOW

0

1

M5

M4

M3

M2

M1

M0

COMMAND

1

1

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

Sym.

Rating

Condition

Supply Voltage

-0.5V ~ 8V

Input Voltage

Output Voltage

Operating Temperature

Storage Temperature