HT46R71D datasheet(13/46 Pages) HOLTEK

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HT46R71D

Rev. 1.00

January 9, 2006

Buzzer Output

The Buzzer function provides a means of producing a

variable frequency output, suitable for applications such

as Piezo-buzzer driving or other external circuits that re-

quire a precise frequency generator. The BZ and BZ

pins form a complimentary pair, and are pin-shared with

I/O pins, PA0 and PA1. A configuration option is used to

select from one of three buzzer options. The first option

is for both pins PA0 and PA1 to be used as normal I/Os,

the second option is for both pins to be configured as BZ

and BZ buzzer pins, the third option selects only the PA0

pin to be used as a BZ buzzer pin with the PA1 pin re-

taining its normal I/O pin function. Note that the BZ pin is

the inverse of the BZ pin which together generate a dif-

ferential output which can supply more power to con-

nected interfaces such as buzzers.

The buzzer is driven by the internal clock source, fS,

which then passes through a divider, the division ratio of

which is selected by configuration options to provide a

range of buzzer frequencies from fS/2

2 to f

S/2

9. The

clock source that generates fS, which in turn controls the

buzzer frequency, can originate from two different

sources, the Int.RCOSC (Internal RC oscillator) or the

System oscillator/4, the choice of which is determined

by the fS clock source configuration option. Note that the

buzzer frequency is controlled by configuration options,

which select both the source clock for the internal clock

fS and the internal division ratio. There are no internal

registers associated with the buzzer frequency.

If the configuration options have selected both pins PA0

and PA1 to function as a BZ and BZ complementary pair

of buzzer outputs, then for correct buzzer operation it is

essential that both pins must be setup as outputs by set-

ting bits PAC0 and PAC1 of the PAC port control regis-

ter to zero. The PA0 data bit in the PA data register must

also be set high to enable the buzzer outputs, if set low,

both pins PA0 and PA1 will remain low. In this way the

single bit PA0 of the PA register can be used as an

on/off control for both the BZ and BZ buzzer pin outputs.

Note that the PA1 data bit in the PA register has no con-

trol over the BZ buzzer pin PA1.

If configuration options have selected that only the PA0

pin is to function as a BZ buzzer pin, then the PA1 pin

can be used as a normal I/O pin. For the PA0 pin to func-

tion as a BZ buzzer pin, PA0 must be setup as an output

by setting bit PAC0 of the PAC port control register to

zero. The PA0 data bit in the PA data register must also

be set high to enable the buzzer output, if set low pin

PA0 will remain low. In this way the PA0 bit can be used

as an on/off control for the BZ buzzer pin PA0. If the

PAC0 bit of the PAC port control register is set high, then

pin PA0 can still be used as an input even though the

configuration option has configured it as a BZ buzzer

output.

Note that no matter what configuration option is chosen

for the buzzer, if the port control register has setup the

pin to function as an input, then this will override the con-

figuration option selection and force the pin to always

behave as an input pin. This arrangement enables the

pin to be used as both a buzzer pin and as an input pin,

so regardless of the configuration option chosen; the ac-

tual function of the pin can be changed dynamically by

the application program by programming the appropri-

ate port control register bit.

D i v i d e r

W D T P r e s c a l e r

M a s k O p t i o n

T i m e - o u t R e s e t

f W D T / 2 1 5 ~ f W D T / 2 1 6

f W D T / 2 1 4 ~ f W D T / 2 1 5

f W D T / 2 1 3 ~ f W D T / 2 1 4

f W D T / 2 1 2 ~ f W D T / 2 1 3

R O M

C o d e

O p t i o n

S y s t e m C l o c k / 4

I n t . R C O S C

f W D T

C K

W D T C l e a r

Watchdog Timer

PAC Register

PAC.0

PAC Register

PAC.1

PA data Register

PA.0

PA data Register

PA.1

Output Function

PA0=0, PA1=0

PA0=BZ, PA1=BZ

PA0=0, PA1=Input

PA0=BZ, PA1=Input

PA0=Input, PA1=0

PA0=Input, PA1=Input

PA0/PA1 Pin Function Control

Note:

²X² stands for don¢t care

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