48R01A3 데이터 시트보기 (PDF) - Holtek Semiconductor

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48R01A3

Small Package I/O Type 8-Bit OTP MCU

Holtek Semiconductor 

HT48R01A

Prescaler

Bits T0PSC0~T0PSC2 of the TMR0C register can be

used to define a division ratio for the internal clock

source of the Timer/Event Counter enabling longer time

out periods to be setup.

Buzzer Function

Operating similar to a programmable frequency divider,

the buzzer function within the microcontroller provides a

means of producing a variable frequency output suitable

for applications, such as piezo-buzzer driving or other

interfaces requiring a precise frequency generator.

BZ and BZ pins are a complimentary pair and pin-shared

with I/O pins, PA0 and PA1. The function is selected via

the CTRL0 register, however, if not selected, the pins can

operate as normal I/O pins. Note that the BZ pin is the in-

verse of the BZ pin generating a kind of differential output

and supplying more power to connected interfaces such

as buzzers. The CTRL0 register can select a single BZ

pin or the complimentary pair BZ and BZ.

The timer overflow signal is the clock source for the

buzzer circuit. The output frequency is controlled by load-

ing the required values into the timer prescaler and timer

registers to give the required division ratio. The counter

will begin to count-up from this preload register value until

full, at which point an overflow signal is generated, caus-

ing both the BZ and BZ outputs to change state. The

counter will then be automatically reloaded with the

preload register value and continue counting- up.

If the CTRL0 register has selected the buzzer function,

then for both buzzer outputs to operate, it is essential

that the Port A control register PAC bit 0 and PAC bit 1

are setup as outputs. If only one pin is setup as an out-

put, the other pin can still be used as a normal data input

pin. However, if both pins are setup as inputs then the

buzzer will not function. The buzzer outputs will only be

activated if bit PA0 is set to ²1². This output data bit is

used as the on/off control bit for the buzzer outputs.

Note that the BZ and BZ outputs will both be low if the

PA0 output data bit is cleared to ²0². The condition of

data bit PA1 has no effect on the overall control of the

BZ and BZ pins.

Using this method of frequency generation, and if a

crystal oscillator is used for the system clock, very pre-

cise values of frequency can be generated.

I/O Interfacing

The Timer/Event Counter, when configured to run in the

event counter or pulse width measurement mode, re-

quires the use of an external timer pin for its operation.

As this pin is a shared pin it must be configured correctly

to ensure that it is setup for use as a Timer/Event Coun-

ter input pin. This is achieved by ensuring that the mode

select bits in the Timer/Event Counter control register,

select either the event counter or pulse width measure-

ment mode. Additionally the corresponding PAC Port

Control Register bit must be set high to ensure that the

pin is setup as an input. Any pull-high resistor connected

to this pin will remain valid even if the pin is used as a

Timer/Event Counter input.

Programming Considerations

When configured to run in the timer mode, the internal

system clock is used as the timer clock source and is

therefore synchronised with the overall operation of the

microcontroller. In this mode when the appropriate timer

register is full, the microcontroller will generate an internal

interrupt signal directing the program flow to the respec-

tive internal interrupt vector. For the pulse width mea-

surement mode, the internal system clock is also used as

the timer clock source but the timer will only run when the

correct logic condition appears on the external timer input

pin. As this is an external event and not synchronised

with the internal timer clock, the microcontroller will only

see this external event when the next timer clock pulse

arrives. As a result, there may be small differences in

measured values requiring programmers to take this into

account during programming. The same applies if the

timer is configured to be in the event counting mode,

which again is an external event and not synchronised

with the internal system or timer clock.

T im e r O v e r flo w

B u z z e r C lo c k

P A 0 D a ta

B Z O u tp u t a t P A 0

B Z O u tp u t a t P A 1

Rev. 1.10

Buzzer Function

20

August 4, 2008

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