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…

CLR

;disable interrupt

MOV

TLx

;read TLx

ADD

#LOW

;LOW is low byte of compensation value

MOV

TLx,

;update TLx

MOV

THx

;read THx

ADDC

#HIGH

;HIGH is high byte of compensation value

MOV

THx,

;update THx

SETB

;enable interrupt

…

(2) Dynamic read counts

When dynamic read running timer count value, if you do not pay attention to could be wrong, this is because it

is not possible at the same time read the value of the TLx and THx. For example the first reading TLx then THx,

because the timer is running, after reading TLx, TLx carry on the THx produced, resulting in error; Similarly,

after the first reading of THx then TLx, also have the same problems.

A kind of way avoid reading wrong is first reading THx then TLx and read THx once more, if the THx twice

to read the same value, then the read value is correct, otherwise repeat the above process. Realization method

reference to the following example code.

…

RDTM: MOV

THx

;save THx to ACC

MOV

R0,

TLx

;save TLx to R0

CJNE

THx,

RDTM

;read THx again and compare with the previous value

MOV

R1,

;save THx to R1

…

7.5 Application note for Timer in practice

(1) Real-time Timer

Timer/Counter start running, When the Timer/Counter is overflow, the interrupt request generated, this

action handle by the hardware automatically, however, the process which from propose interrupt request to

respond interrupt request requires a certain amount of time, and that the delay interrupt request on-site with

the environment varies, it normally takes three machine cycles of delay, which will bring real-time processing

bias. In most occasions, this error can be ignored, but for some real-time processing applications, which

require compensation.

Such as the interrupt response delay, for timer mode 0 and mode 1, there are two meanings: the first,

because of the interrupt response time delay of real-time processing error; the second, if you require multiple

consecutive timing, due to interruption response delay, resulting in the interrupt service program once again

sets the count value is delayed by several count cycle.

If you choose to use Timer/Counter mode 1 to set the system clock, these reasons will produce real-time

error for this situation, you should use dynamic compensation approach to reducing error in the system clock,

compensation method can refer to the following example program.

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