HT56R656 datasheet(43/108 Pages) HOLTEK

43 / 108 page

HT56R62/HT56R65

HT56R642/HT56R644/HT56R654/HT56R656

Rev. 1.00

July 20, 2009

Device

HT56R62

HT56R642/HT56R644

HT56R65/HT56R654/HT56R656

No. of 8-bit Timers

Timer Name

Timer/Event Counter 0

Timer/Event Counter 1

Timer/Event Counter 0

Timer/Event Counter2

Timer Register Name

TMR0

TMR1

TMR0

TMR2

Control Register Name

TMR0C

TMR1C

TMR0C

TMR2C

No. of 16-bit Timers

Timer Name

Timer/Event Counter 1

Timer Register Name

TMR1L/TMR1H

Control Register Name

TMR1C

Timer Registers

- TMR0, TMR1, TMR1L/TMR1H,

TMR2

The timer registers are special function registers located in

the Special Purpose Data Memory and is the place where

the actual timer value is stored. For the 8-bit Timer/Event

Counters, these registers are known as TMR0, TMR1 or

TMR2. For the 16-bit Timer/Event Counter, a pair of regis-

ters are required and are known as TMR1L/TMR1H. The

value in the timer registers increases by one each time an

internal clock pulse is received or an external transition oc-

curs on the external timer pin. The timer will count from the

initial value loaded by the preload register to the full count

of FFH for the 8-bit timer or FFFFH for the 16-bit timer at

which point the timer overflows and an internal interrupt

signal is generated. The timer value will then be reset with

the initial preload register value and continue counting.

To achieve a maximum full range count of FFH for the

8-bit timer or FFFFH for the 16-bit timer, the preload reg-

isters must first be cleared to all zeros. It should be

noted that after power-on, the preload register will be in

an unknown condition. Note that if the Timer/Event

Counter is switched off and data is written to its preload

registers, this data will be immediately written into the

actual timer registers. However, if the Timer/Event

Counter is enabled and counting, any new data written

into the preload data registers during this period will re-

main in the preload registers and will only be written into

the timer registers the next time an overflow occurs.

For the 16-bit Timer/Event Counter which has both low

byte and high byte timer registers, accessing these reg-

isters is carried out in a specific way. It must be noted

when using instructions to preload data into the low byte

timer register, the data will only be placed in a low byte

buffer and not directly into the low byte timer register.

The actual transfer of the data into the low byte timer

high byte timer register, namely TMR1H, is executed.

On the other hand, using instructions to preload data

into the high byte timer register will result in the data be-

ing directly written to the high byte timer register. At the

same time the data in the low byte buffer will be trans-

ferred into its associated low byte timer register. For this

reason, the low byte timer register should be written first

when preloading data into the 16-bit timer registers. It

must also be noted that to read the contents of the low

byte timer register, a read to the high byte timer register

must be executed first to latch the contents of the low

byte timer register into its associated low byte buffer. Af-

ter this has been done, the low byte timer register can be

read in the normal way. Note that reading the low byte

timer register will result in reading the previously latched

contents of the low byte buffer and not the actual con-

tents of the low byte timer register.

Timer Control Registers

- TMR0C, TMR1C, TMR2C

The flexible features of the Holtek microcontroller

Timer/Event Counters enable them to operate in three

different modes, the options of which are determined by

the contents of their respective control register.

It is the Timer Control Register together with its corre-

sponding timer registers that control the full operation of

the Timer/Event Counters. Before the timers can be

used, it is essential that the appropriate Timer Control

sure its correct operation, a process that is normally car-

ried out during program initialisation.

To choose which of the three modes the timer is to oper-

ate in, either in the timer mode, the event counting mode

or the pulse width measurement mode, bits 7 and 6 of

the corresponding Timer Control Register, which are

known as the bit pair TnM1/TnM0, must be set to the re-

quired logic levels. The timer-on bit, which is bit 4 of the

Timer Control Register and known as TnON, depending

upon which timer is used, provides the basic on/off con-

trol of the respective timer. Setting the bit high allows the

counter to run, clearing the bit stops the counter. For tim-

ers that have prescalers, bits 0~2 of the Timer Control

HT56R656 数据表(PDF) 43 Page - Holtek Semiconductor Inc

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