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48R01A1

Small Package I/O Type 8-Bit OTP MCU

Holtek Semiconductor 

HT48R01A

In addition, on entering an interrupt sequence or execut-

ing a subroutine call, the status register will not be

pushed onto the stack automatically. If the contents of

the status registers are important and if the interrupt rou-

tine can change the status register, precautions must be

taken to correctly save it.

Interrupt Control Registers - INTC0

The 8-bit register, known as INTC0, control the opera-

tion of both external, and internal timer interrupts. By

setting various bits within this register using standard bit

manipulation instructions, the enable/disable function of

each interrupt can be independently controlled. A mas-

ter interrupt bit within this register, the EMI bit, acts like a

global enable/disable and is used to set all of the inter-

rupt enable bits on or off. This bit is cleared when an in-

terrupt routine is entered to disable further interrupt and

is set by executing the ²RETI² instruction.

Timer/Event Counter Register

The device contains one integrated 8-bit Timer/Event

Counter. An associated register known as TMR0 is the

location where the timer¢s 8-bit value is located. An as-

sociated control register, known as TMR0C, contains

the setup information for this timer.

Input/Output Ports and Control Registers

Within the area of Special Function Registers, the port

PA data I/O register and its associated control register

PAC play a prominent role. These registers are mapped

to specific addresses within the Data Memory as shown

in the Data Memory table. The PA data I/O register, is

used to transfer the appropriate output or input data on

the PA port. The PAC control register specifies which

pins of PA are set as inputs and which are set as out-

puts. To setup a pin as an input, the corresponding bit of

the control register must be set high, for an output it

must be set low. During program initialisation, it is impor-

tant to first setup the control registers to specify which

pins are outputs and which are inputs before reading

data from or writing data to the I/O ports. One flexible

feature of these registers is the ability to directly pro-

gram single bits using the ²SET [m].i² and ²CLR [m].i²

instructions. The ability to change I/O pins from output to

input and vice versa by manipulating specific bits of the

I/O control registers during normal program operation is

a useful feature of these devices.

System Control Register - CTRL0

This register is used to provide control over certain inter-

nal functions including certain system clock options, the

buzzer selection control and an RTC Oscillator quick

start up function.

When the buzzer function, BZ or BZ, is disabled, then

these two pins will have a normal I/O function. If en-

abled, the BZ or BZ outputs will still be controlled by the

related I/O port control and data settings.

System Control Register - CTRL1

This register is used to provide control over certain inter-

nal functions including the External Interrupt edge trig-

ger type and the Watchdog Timer control function.

Wake-up Function Register - PAWK

When the microcontroller enters the Power Down Mode,

various methods exist to wake the device up and con-

tinue with normal operation. One method is to allow a

low going edge on the I/O pins to have a wake-up func-

tion. This register is used to select which I/O pins are

used to have this wake-up function.

Pull-high Register - PAPU

The I/O pins, if configured as inputs, can have internal

pull-high resistors connected, which eliminates the need

for external pull-high resistors. This register selects which

I/O pins are connected to internal pull-high resistors.

Rev. 1.10

13

August 4, 2008

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