HT45R35 datasheet(16/59 Pages) HOLTEK

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HT45R35

Rev. 1.30

May 14, 2010

Timer/Event Counter

An 8-bit timer/event counter, known as Timer/Event

Counter, is implemented in the microcontroller. The

Timer/Event Counter contains an 8-bit programmable

count-up counter whose clock may come from an exter-

nal source or from the system clock. Using the external

clock input allows the user to count external events, mea-

sure time internals or pulse widths, or generate an accu-

rate time base. Using the internal clock allows the user to

generate an accurate time base.

There are 2 registers related to the Timer/Event Coun-

ter, TMR and TMRC. Two physical registers are mapped

to the TMR location; writing to TMR places the start

value of the Timer/Event Counter in a preload register

while reading TMR retrieves the contents of the

Timer/Event Counter. The TMRC is a timer/event coun-

ter control register, which defines the timer operating

conditions.

The TM0, TM1 bits define the operating mode. The event

count mode is used to count external events, which

means the clock source comes from an external TMR

pin. The timer mode functions as a normal timer with the

clock source coming from the fINT clock. The pulse width

measurement mode can be used to measure the high or

low level duration of an external signal on the TMR pin.

The counting is based on the fINT clock source. In the

event counting or timer mode, once the timer/event coun-

ter starts counting, it will count from the current contents

in the Timer/Event Counter to FFH. Once overflow oc-

curs, the counter is reloaded from the Timer/Event Coun-

ter preload register and an interrupt request flag TF; bit 5

of INTC0, is generated at the same time.

In the pulse width measurement mode, with the TON

and TE bits equal to one, once the TMR pin has re-

ceived a transient from low to high, or high to low if the

TE bit is 0, it will start counting until the TMR pin returns

to its original level and resets the TON bit. The mea-

sured result will remain in the Timer/Event Counter even

if the activated transient occurs again. Therefore, only a

single shot measurement can be made. The TON bit

must be set again by software for further measurements

T M 1

T M 0

T M R

T E

T M 1

T M 0

T O N

P u l s e W i d t h

M e a s u r e m e n t

M o d e C o n t r o l

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

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

8 - B i t T i m e r / E v e n t

C o u n t e r ( T M 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

7 - S t a g e P r e s c a l e r

8 - 1 M U X

f I N T

T P S C 2 ~ T P S C 0

S y s t e m C l o c k

Timer/Event Counter

Bit No.

Label

Function

0~2

TPSC0~TPSC2

To define the prescaler stages, TPSC2, TPSC1, TPSC0=

000: fINT=fSYS

001: fINT=fSYS/2

010: fINT=fSYS/4

011: fINT=fSYS/8

100: fINT=fSYS/16

101: fINT=fSYS/32

110: fINT=fSYS/64

111: fINT=fSYS/128

3TE

To define the TMR active edge of the timer/event counter

(0=active on low to high; 1=active on high to low)

TON

To enable or disable timer counting (0=disabled; 1=enabled)

Unused bit, read as

²0²

TM0

TM1

To define the operating mode, TM1, TM0=

01=Event count mode (external clock)

10=Timer mode (internal clock)

11=Pulse width measurement mode

00=Unused

TMRC (0EH) Register

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