HT82K74EE datasheet(20/56 Pages) HOLTEK

20 / 56 page

HT82K74E/HT82K74EE

Rev. 1.00

December 15, 2009

the correct value into the port control register or by pro-

gramming individual bits in the port control register us-

ing 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.

All I/O ports have the capability of providing wake-up

functions. When the device is in the Power Down Mode,

various methods are available to wake the device up.

One of these is a transition of any of the selected

wake-up pins.

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 an inter-

nal 16-bit count-up timer which has three operating

modes. The timer can be configured to operate as a

general timer, external event counter or as a pulse width

measurement device.

There are three registers related to the Timer/Event

Counter, TMRL, TMRH and TMRC. The TMRL/TMRH

timing value. Writing to this register pair places an initial

starting value in the Timer/Event Counter preload regis-

ter while reading retrieves the contents of the

Timer/Event Counter. The TMRC register is a

Timer/Event Counter control register, which defines the

timer options, and determines how the timer is to be

used. The timer clock source can be configured to come

from the internal system clock divided by 4 or from an

external clock on shared pin PA2/TMR.

Configuring the Timer/Event Counter Input Clock

Source

The timer clock source can originate from either the sys-

tem clock divided by 4 or from an external clock source.

The system clock divided by 4 is used when the timer is

in the timer mode or in the pulse width measurement

mode.

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

event counting mode, the clock source being provided

on shared pin PA2/TMR. Depending upon the condition

of the TE bit, each high to low, or low to high transition on

the PA2/TMR pin will increment the counter by one.

Timer Registers

- TMRH, TMRL

The TMRH and TMRL registers are two 8-bit special

function register locations within the special purpose

Data Memory where the actual timer value is stored.

The value in the timer counter increases by one each

time an internal clock pulse is received or an external

transition occurs on the PA2/TMR pin. The timer will

count from the initial value loaded by the preload regis-

ter to the full count value of FFFFH at which point the

timer overflows and an internal interrupt signal gener-

ated. The timer value will then be reset with the initial

preload register value and continue counting. For a

maximum full range count of 0000H to FFFFH the

preload registers must first be cleared to 0000H. It

should be noted that after power-on the preload regis-

ters will be in an unknown condition. Note that if the

Timer/Event Counter is not running and data is written to

its preload registers, this data will be immediately written

into the actual counter. However, if the counter is en-

abled and counting, any new data written into the

preload registers during this period will remain in the

preload registers and will only be written into the actual

counter the next time an overflow occurs.

Accessing these registers is carried out in a specific

way. It must be noted that when using instructions to

preload data into the low byte register, namely TMRL,

the data will only be placed in a low byte buffer and not

directly into the low byte register. The actual transfer of

the data into the low byte register is only carried out

when a write to its associated high byte register, namely

TMRH, is executed. On the other hand, using instruc-

tions to preload data into the high byte timer register will

result in the data being directly written to the high byte

will be transferred into its associated low byte register.

For this reason, when preloading data into the 16-bit

timer registers, the low byte should be written first. It

T E

T M R

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 O N

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 M 1 T M 0

f S Y S / 4

16-bit Timer/Event Counter Structure

HT82K74EE Datasheet(PDF) 20 Page - Holtek Semiconductor Inc

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