HT45R35 datasheet(18/59 Pages) HOLTEK

18 / 59 page

HT45R35

Rev. 1.30

May 14, 2010

the Timer A/Timer B (16-bit) simultaneously. Timer

A/Timer B is changed by writing to TMRAH/TMRBH but

writing to TMRAL/TMRBL will keep the Timer A/Timer B

unchanged.

Reading TMRAH/TMRBH will also latch the

TMRAL/TMRBL into the low byte buffer to avoid false

timing problem. Reading TMRAL/TMRBL returns the

contents of the low byte buffer. Therefore, the low byte

of Timer A/Timer B can not be read directly. It must read

TMRAH/TMRBH first to ensure that the low byte con-

tents of Timer A/Timer B are latched into the buffer.

The resistor and capacitor form an oscillation circuit and

input to TMRBH and TMRBL. The RCOM0, RCOM1

and RCOM2 bits of RCOCCR define the clock source of

Timer A. It is recommended that the clock source of

Timer A uses the system clock or the instruction clock.

If the RCOCON bit, bit 4 of RCOCCR, is set to

²1², Timer

A and Timer B will start counting until Timer A or Timer B

overflows, the timer/event counter will then generate an

interrupt request flag which is RCOCF; bit 4 of INTC1.

The Timer A and Timer B will stop counting and will reset

the RCOCON bit to

²0² at the same time. If the

RCOCON bit is

²1², TMRAH, TMRAL, TMRBH and

TMRBL cannot be read or written.

External RC oscillation converter mode example program - Timer A overflow:

clr RCOCCR

mov a, 00000010b

; Enable External RC oscillation mode and set Timer A overflow

mov RCOCR,a

clr intc1.4

; Clear External RC Oscillation Converter interrupt request flag

mov a, low (65536-1000)

; Give timer A initial value

mov tmral, a

; Timer A count 1000 time and then overflow

mov a, high (65536-1000)

mov tmrah, a

mov a, 00h

; Give timer B initial value

mov tmrbl, a

mov a, 00h

mov tmrbh, a

mov a, 00110000b

; Timer A clock source=fSYS/4 and timer on

mov RCOCCR, a

p10:

clr wdt

snz intc1.4

; Polling External RC Oscillation Converter interrupt request flag

jmp p10

clr intc1.4

; Clear External RC Oscillation Converter interrupt request flag

; Program continue

T i m e r A

T i m e r B

O V B = 1

O V B = 0

E x t e r n a l R C O s c i l l a t i o n C o n v e r t e r I n t e r r u p t

R e s e t R C O C O N

R C O S C O u t p u t

S 2

S 1

S y s t e m C l o c k

S y s t e m C l o c k / 4

R C O C O N

External RC Oscillation Converter

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