HT83F02 datasheet(22/64 Pages) HOLTEK

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HT83F02

Rev. 1.20

November 19, 2010

Timer Control Registers

- TMR0C, TMR1C

Each timer has its respective timer control register,

known as TMR0C and TMR1C. It is the timer control

that control the full operation of the timers. Before the

timers can be used, it is essential that the appropriate

timer control register is fully programmed with the right

data to ensure its correct operation, a process that is

normally carried out during program initialization. Bits 7

and 6 of the Timer Control Register, must be set to the

required logic levels. Bit 6 of the registers must always

be written with a

²1², and bit 7 must always be written

with a

²0². The timer-on bit, which is bit 4 of the Timer

Control Register and known as T0ON/ T1ON, depend-

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

control of the respective timer. setting the bit high allows

the timer to run, clearing the bit stops the timer. For the

8-bit timers, which have prescalers, bits 0~2 of the

Timer Control Register determines the division ratio of

the input clock prescaler.

Configuring the Timer

The Timer is used to measure fixed time intervals, pro-

viding an internal interrupt signal each time the Timer

overflows. To do this the Operating Mode Select bit pair

in the Timer Control Register must be set to the correct

value as shown.

Control Register Operating Mode

Select Bits

Bit7 Bit6

The internal clock, f

SYS, is used as the Timer clock. How-

ever, this clock source is further divided by a prescaler,

the value of which is determined by the Prescaler Rate

Select bits, which are bits 0~2 in the Timer Control Reg-

ister. After the other bits in the Timer Control Register

have been setup, the enable bit, which is bit 4 of the

Timer Control Register, can be set high to enable the

Timer to run. Each time an internal clock cycle occurs,

the Timer increments by one. When it is full and over-

flows, an interrupt signal is generated and the Timer will

reload the value already loaded into the preload register

and continue counting. The interrupt can be disabled by

ensuring that the Timer Interrupt Enable bit in the Inter-

rupt Control Register, INTC, is reset to zero.

Prescaler

All of the 8-bit timers possess a prescaler. Bits 0~2 of

their associated timer control register, define the

pre-scaling stages of the internal clock source of the

Timer. The Timer overflow signal can be used to gener-

ate signals for the Timer interrupt.

Programming Considerations

The internal system clock is used as the timer clock

source and is therefore synchronized with the overall

operation of the microcontroller. In this mode, when the

appropriate timer register is full, the microcontroller will

generate an internal interrupt signal directing the pro-

gram flow to the respective internal interrupt vector.

When the Timer is read, the clock is blocked to avoid er-

rors, however as this may result in a counting error, this

should be taken into account by the programmer. Care

must be taken to ensure that the timers are properly ini-

tialized before using them for the first time. The associ-

ated timer enable bits in the interrupt control register must

be properly set otherwise the internal interrupt associated

with the timer will remain inactive. The edge select, timer

mode and clock source control bits in timer control regis-

ter must also be correctly set to ensure the timer is prop-

erly configured for the required application. It is also

important to ensure that an initial value is first loaded into

the timer registers before the timer is switched on; this is

because after power-on the initial values of the timer reg-

isters are unknown. After the timer has been initialized

the timer can be turned on and off by controlling the en-

able bit in the timer control register.

I n c r e m e n t

T i m e r C o n t r o l l e r

P r e s c a l e r O u t p u t

T i m e r + 1

T i m e r + 2

T i m e r + N

T i m e r + N + 1

Timer Mode Timing Diagram

HT83F02 Datasheet(PDF) 22 Page - Holtek Semiconductor Inc

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