HT46R01A datasheet(17/58 Pages) HOLTEK

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HT46R01A

Rev. 1.10

August 13, 2008

Programming Considerations

Within the user program, one of the first things to con-

sider is port initialisation. After a reset, the PA data regis-

ter and PAC port control register will be set high. This

means that all I/O pins will default to an input state, the

level of which depends on the other connected circuitry

and whether pull-high options have been selected. If the

PAC port control register, is then programmed to setup

some pins as outputs, these output pins will have an ini-

tial high output value unless the associated PA port data

puts and which are outputs can be achieved byte-wide

by loading the correct value into the port control register

or by programming individual bits in the port control reg-

ister using the

²SET [m].i² and ²CLR [m].i² instructions.

Note that when using these bit control instructions, a

read-modify-write operation takes place. The

microcontroller must first read in the data on the entire

port, modify it to the required new bit values and then re-

write this data back to the output ports.

Pins PA0 to PA7 each have a wake-up functions, se-

lected via the PAWK register. When the device is in the

Power Down Mode, various methods are available to

wake the device up. One of these is a high to low transi-

tion of any of the these pins. Single or multiple pins on

Port A can be setup to have this function.

Timer/Event Counter

The provision of timers form an important part of any

microcontroller, giving the designer a means of carrying

out time related functions. This device contains one

count-up timer of 8-bit capacity. As the timer has three

different operating modes, it can be configured to oper-

ate as a general timer, an external event counter or as a

pulse width measurement device. The provision of an

internal prescaler to the clock circuitry gives added

range to the timer.

There are two types of registers related to the

Timer/Event Counter. The first is the register that con-

tains the actual value of the Timer/Event Counter and

into which an initial value can be preloaded. Reading

from this register retrieves the contents of the

Timer/Event Counter. The second type of associated

timer options and determines how the timer is to be

used. The device can have the timer clock configured to

come from the internal clock source. In addition, the

timer clock source can also be configured to come from

an external timer pin.

An external clock source is used when the timer is in the

event counting mode, the clock source being provided

on the external timer pin, known as TMR0. These exter-

nal timer pins are pin-shared with other I/O pins. De-

pending upon the condition of the T0E bit in the

corresponding Timer Control Register, each high to low,

or low to high transition on the external timer input pin

will increment the counter by one.

Configuring the Timer/Event Counter Input Clock

Source

The internal timer

¢s clock can originate from various

sources, depending upon which device and which timer

is chosen. The system clock input timer source is used

when the timer is in the timer mode or in the pulse width

measurement mode. This system clock timer source is

first divided by a prescaler, the division ratio of which is

conditioned by the Timer Control Register bits

T0PSC0~T0PSC2.

T 1

T 2

T 3

T 4

T 1

T 2

T 3

T 4

W r i t e t o P o r t

R e a d f r o m P o r t

S y s t e m C l o c k

P o r t D a t a

Read/Write Timing

T M R 0

T 0 E

T i m e r / E v e n t C o u n t e r

M o d e C o n t r o l

T 0 O N

P r e l o a d R e g i s t e r

T i m e r / E v e n t C o u n t e r

D a t a B u s

R e l o a d

O v e r f l o w

t o I n t e r r u p t

P F D o r B u z z e r

8 - s t a g e p r e s c a l e r

T 0 P S C 2 ~ T 0 P S C 0

( 1 / 2 ~ 1 / 2 5 6 )

T 0 M 1

T 0 M 0

f S Y S

R T C O s c i l l a t o r

T 0 S

8-bit Timer/Event Counter Structure

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