HT86B05 datasheet(38/79 Pages) HOLTEK

38 / 79 page

HT86BXX/HT86BRXX

Rev. 1.60

October 20, 2009

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.

Timer Program Example

The following example program section is based on the

HT86B40, HT86B50, HT86B60, HT86BR60, HT86B70,

HT86B80 and HT86B90 devices, which contain a single

internal 16-bit timer. Programming the timer for other de-

vices is conducted in a very similar way. The program

shows how the timer registers are setup along with how

the interrupts are enabled and managed. Points to note

in the example are how, for the 16-bit timer, the low byte

must be written first, this is because the 16-bit data will

only be written into the actual timer register when the

high byte is loaded. 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.

#include HT86B40.inc

jmp begin

org 04h

; external interrupt vectors

reti

org 08h

reti

org 0Ch

reti

org 10h

; timer 2 interrupt vector

jmp tmr2int

; jump here when timer 2 overflows

org 14h

reti

; internal timer 2 interrupt routine

tmr2int:

; timer 2 main program placed here

reti

begin:

; setup timer 2 registers

mov a,09bh

; setup timer 2 low byte

mov tmr2l,a

; low byte must be setup before high byte

mov a,0e8h

; setup timer 2 high byte

mov tmr2h,a

; setup timer 2 high byte

mov a,090h

; setup timer 2 control register

mov tmr2c,a

; setup timer mode

; setup interrupt register

mov a,01h

; enable master interrupt

mov intc,a

mov a,01h

; enable timer 2 interrupt

mov intch,a

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