48R01A1 Ver la hoja de datos (PDF) - Holtek Semiconductor

Número de pieza

componentes Descripción

Fabricante

48R01A1

Small Package I/O Type 8-Bit OTP MCU

Holtek Semiconductor 

HT48R01A

When the Timer/Event Counter is read, or if data is writ-

ten to the preload register, the clock is inhibited to avoid

errors, 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 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 initialised

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

able bit in the timer control register.

When the Timer/Event Counter overflows, its corre-

sponding interrupt request flag in the interrupt control

register will be set. If the Timer/Event Counter interrupt

is enabled this will in turn generate an interrupt signal.

However irrespective of whether the interrupts are en-

abled or not, a Timer/Event Counter overflow will also

generate a wake-up signal if the device is in a

Power-down condition. This situation may occur if the

Timer/Event Counter is in the Event Counting Mode and

if the external signal continues to change state. In such

a case, the Timer/Event Counter will continue to count

these external events and if an overflow occurs the de-

vice will be woken up from its Power-down condition. To

prevent such a wake-up from occurring, the timer inter-

rupt request flag should first be set high before issuing

the ²HALT² instruction to enter the Power Down Mode.

Timer Program Example

The program shows how the Timer/Event Counter regis-

ters are setup along with how the interrupts are enabled

and managed. Note how the Timer/Event Counter is

turned on, by setting bit 4 of the Timer Control Register.

The Timer/Event Counter can be turned off in a similar

way by clearing the same bit. This example program

sets the Timer/Event Counters to be in the timer mode,

which uses the internal system clock as their clock

source.

:

org 04h

:

; external interrupt vector

org 08h

; Timer Counter 0 interrupt vector

jmp tmr0int

; jump here when Timer 0 overflows

:

:

org 20h

; main program

:

:

;internal Timer 0 interrupt routine

tmr0int:

:

; Timer 0 main program placed here

:

:

begin:

;setup Timer 0 registers

mov a,09bh

; setup Timer 0 preload value

mov tmr0,a

mov a,081h

; setup Timer 0 control register

mov tmr0c,a

; timer mode and prescaler set to /2

;setup interrupt register

mov a,00dh

; enable master interrupt and both timer interrupts

mov intc0,a

:

:

set tmr0c.4

; start Timer 0

:

:

Rev. 1.10

21

August 4, 2008

Share Link: