HT95R22 datasheet(17/52 Pages) HOLTEK

17 / 52 page

HT95R22

Rev. 1.00

January 6, 2009

Timer/Event Counters

The provision of timers form an important part of any

microcontroller, giving the designer a means of carrying

out time related functions. The device contains two

count-up timers of 16-bit capacity. One of these timers

has three different operating modes, and can be config-

ured to operate as a general timer, an external event

counter or as a pulse width measurement device.

There are two types of registers related to the

Timer/Event Counters. The first are the registers that

contains the actual value of the Timer/Event Counter

and into which an initial value can be preloaded, and are

known as TMR0L/TMR0H and TMR1L/TMR1H. Read-

ing these register pairs retrieves the contents of the

Timer/Event Counters. The second type of associated

the timer options and determines how the Timer/Event

Counters are to be used, and have the name TMR0C

and TMR1C. Timer/Event Counter 0 can have its timer

clock configured to come from the internal clock source

or from an external timer pin.

Configuring the Timer/Event Counter Input Clock

Source

For Timer/Event Counter 0, the internal timer clock

source can originate from either the system clock/4 sys-

tem clock or from an external clock source. For

Timer/Event Counter 1, the internal timer clock source

originates from the 32768Hz system clock. The system

clock input timer source is used when the Timer/Event

Counters 1 is in the timer mode or for Timer/Event Coun-

ter 0, when also in the pulse width measurement mode.

An external clock source is used when the Timer/Event

Counter 0 is in the event counting mode, the clock

source being provided on the external timer pin TMR0.

Depending upon the condition of the T0E bit, each high

to low, or low to high transition on the external timer pin

will increment the counter by one.

Timer Registers

- TMR0L/TMR0H, TMR1L/TMR1H

The timer registers are special function register pairs

located in the Special Purpose Data Memory and is the

place where the 16-bit actual timer value is stored.

These register pairs are known as TMR0L/TMR0H and

TMR1L/TMR1H. The value in the timer register pair

increases by one each time an internal clock pulse is

received or an external transition occurs on the external

timer pin. The timer will count from the initial value

loaded by the preload register to the full count of FFFFH

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 FFFFH the

preload register 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 register, this data will be immediately writ-

ten into the actual timer register. However, if the

Timer/Event Counter is enabled and counting, any new

data written into the preload data register during this pe-

1 6 - b i t

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

L o w B y t e B u f f e r

H i g h B y t e

L o w B y t e

1 6 - B i t T i m e r / E v e n t C o u n t e r

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

f S Y S / 4

T 0 M 1

T 0 M 0

16-bit Timer/Event Counter 0 Structure

1 6 - b i t

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

L o w B y t e B u f f e r

H i g h B y t e

L o w B y t e

1 6 - B i t T i m e r / E v e n t C o u n t e r

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 1 O N

3 2 7 6 8 H z

T 1 M 1

T 1 M 0

16-bit Timer/Event Counter 1 Structure

HT95R22 Datasheet(PDF) 17 Page - Holtek Semiconductor Inc

HT95R22 Datasheet(HTML) 17 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

Datasheet Download

Link URL