HT86B50 datasheet(56/83 Pages) HOLTEK

56 / 83 page

HT86BXX/HT86BRXX

Rev. 1.80

March 12, 2010

T i m e r 2

T i m e r 4

R C O C O N

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

f S Y S / 4

C l o c k

S e l e c t

f S Y S

R C O M O B i t

Programming Considerations

As the 16-bit Timers have both low byte and high byte

timer registers, accessing these registers is carried out

in a specific way. It must be noted that when using in-

structions to preload data into the low byte registers,

namely TMR2L or TMR4L, the data will only be placed

into a low byte buffer and not directly into the low byte

high byte register, namely TMR2H or TMR4H, is exe-

cuted. However, using instructions to preload data into

the high byte timer register will result in the data being

directly written to the high byte register. At the same time

the data in the low byte buffer will be transferred into its

associated low byte register. For this reason, when

preloading data into the 16-bit timer registers, the low

byte should be written first. It must also be noted that to

read the contents of the low byte register, a read to the

high byte register must first be executed to latch the con-

tents of the low byte buffer into its associated low byte

can be read in the normal way. Note that reading the low

byte timer register will only result in reading the previ-

ously latched contents of the low byte buffer and not the

actual contents of the low byte timer register.

Program Example

External RC oscillation converter mode example program

- Timer 2 overflow:

clr

RCOCCR

mov

a, 00000010b

; Enable External RC oscillation mode and set Timer 2

; overflow interrupt

mov

RCOCR,a

clr

intch.4

; Clear External RC Oscillation Converter interrupt

; request flag

mov

a, low (65536-1000); Give timer 2 initial value

mov

Tmr2l, a

; Timer 2 count 1000 time and then overflow

mov

a, high (65536-1000)

mov

Tmr2h, a

mov

a, 00h

; Give timer 4 initial value

mov

Tmr4l, a

mov

a, 00h

mov

Tmr4h, a

mov

a, 00110000b

; Timer 2 clock source=fSYS/4 and timer on

mov

RCOCCR, a

p10:

clr

Wdt

snz

intch.4

; Polling External RC Oscillation Converter interrupt

; request flag

jmp

p10

clr

intch.4

; Clear External RC Oscillation Converter interrupt

; request flag

; Program continue

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