HT47C20 datasheet(23/56 Pages) HOLTEK

23 / 56 page

HT47C20

January 18, 2000

It is strongly recommended to load first the de-

sired value for TMRBL, TMRBH, TMRAL, and

TMRAH registers, before turning on the re-

lated timer/event counter for proper operation.

Because the initial value of TMRBL, TMRBH,

TMRAL and TMRAH are unknown.

If the timer/event counter is on, the TMRAH,

TMRAL, TMRBH and TMRBL cannot be read

or written to. Only when the timer/event coun-

ter is off and when the instruction ²MOV² is

used could those four registers be read or writ-

ten to.

Example for Timer/event counter mode (disable interrupt):

clr tmrc

clr adcr.1

; set timer mode

clr intc1.4

; clear timer/event counter interrupt request flag

mov a, low (65536-1000)

; give timer initial value

mov tmrbl, a

; count 1000 time and then overflow

mov a, high (65536-1000)

mov tmrbh, a

mov a, 00110000b

; timer clock source=T1 and timer on

mov tmrc, a

p10:

clr wdt

snz intcl.4

; polling timer/event counter interrupt request flag

jmp p10

clr intcl.4

; clear timer/event counter interrupt request flag

; program contimue

HT47C20 Datasheet(PDF) 23 Page - Holtek Semiconductor Inc