HT86A72 datasheet(29/68 Pages) HOLTEK

29 / 68 page

HT86Axx/HT86ARxx

Rev. 1.00

March 19, 2010

b 7

T O N

T M 0

T M 1

b 0

N o t i m p l e m e n t e d , r e a d a s " 0 "

T i m e r o n / o f f c o n t r o l

1 : e n a b l e

0 : d i s a b l e

O p e r a t i n g M o d e S e l e c t

T 0 T M 1

T 1 T M 1

T 2 T M 1

T 3 T M 1

T 0 T M 0

T 1 T M 0

T 2 T M 0

T 3 T M 0

n o m o d e a v a i l a b l e

t i m e r m o d e

n o m o d e a v a i l a b l e

T M R 0 C / T M R 1 C / T M R 2 C / T M R 3 C R e g i s t e r

N o t i m p l e m e n t e d , r e a d a s " d o n ' t c a r e "

P S C 2

P S C 1

P S C 0

T i m e r P r e s c a l e r R a t e S e l e c t

T 0 P S C 2

T 1 P S C 2

T 2 P S C 2

T 3 P S C 2

T 0 P S C 1

T 1 P S C 1

T 2 P S C 1

T 3 P S C 1

T 0 P S C 0

T 1 P S C 0

T 2 P S C 0

T 3 P S C 0

T i m e r R a t e

1 : 2

1 : 4

1 : 8

1 : 1 6

1 : 3 2

1 : 6 4

1 : 1 2 8

1 : 2 5 6

Timer Control Register

- All Devices

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 in-

itialised 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 as-

sociated with the timer will remain inactive. It is also im-

portant 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

registers are unknown. After the timer has been initial-

ised the timer can be turned on and off by controlling the

enable bit in the timer control register.

Timer Program Example

The following example program section is based on the

devices, which contain a single internal 8-bit timer. Pro-

gramming the timer for other devices is conducted in a

very similar way. The program shows how the timer reg-

isters are setup along with how the interrupts are en-

abled and managed. Also note how the timer is turned

on by setting bit 4 of the respective timer control register.

The timer can be turned off in a similar way by clearing

the same bit. This example program sets the timer to be

in the timer mode which uses the internal system clock

as their clock source.

HT86A72 Datasheet(PDF) 29 Page - Holtek Semiconductor Inc

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