參數(shù)資料
型號： PIC16CR7X
廠商： Microchip Technology Inc.
英文描述： 28/40-Pin, 8-Bit CMOS ROM Microcontrollers
中文描述： 28/40-Pin，8位微控制器的CMOS光盤
文件頁數(shù)： 51/172頁
文件大?。?/td> 1506K
代理商： PIC16CR7X
2007 Microchip Technology Inc.
DS21993C-page 49
PIC16CR7X
6.4
Timer1 Operation in
Asynchronous Counter Mode
If control bit T1SYNC (T1CON<2>) is set, the external
clock input is not synchronized. The timer continues to
increment asynchronous to the internal phase clocks.
The timer will continue to run during Sleep and can
generate an interrupt on overflow, which will wake-up
the processor. However, special precautions in soft-
ware are needed to read/write the timer (
Section 6.4.1
“Reading and writing Timer1 in asynchronous
counter mode”
).
In Asynchronous Counter mode, Timer1 cannot be
used as a time base for capture or compare operations.
6.4.1
READING AND WRITING TIMER1 IN
ASYNCHRONOUS COUNTER
MODE
Reading TMR1H or TMR1L, while the timer is running
from an external asynchronous clock, will ensure a
valid read (taken care of in hardware). However, the
user should keep in mind that reading the 16-bit timer
in two 8-bit values itself, poses certain problems, since
the timer may overflow between the reads.
For writes, it is recommended that the user simply stop
the timer and write the desired values. A write conten-
tion may occur by writing to the timer registers, while
the register is incrementing. This may produce an
unpredictable value in the timer register.
Reading the 16-bit value requires some care. The
example
code
provided
Example 6-2 demonstrates how to write to and read
Timer1 while it is running in Asynchronous mode.
in
Example 6-1
and
EXAMPLE 6-1:
WRITING A 16-BIT FREE-RUNNING TIMER
EXAMPLE 6-2:
; All interrupts are disabled
MOVF
TMR1H, W
MOVWF
TMPH
MOVF
TMR1L, W
MOVWF
TMPL
MOVF
TMR1H, W
SUBWF
TMPH, W
BTFSC
STATUS,Z
GOTO
CONTINUE
; TMR1L may have rolled over between the read of the high and low bytes.
; Reading the high and low bytes now will read a good value.
MOVF
TMR1H, W
; Read high byte
MOVWF
TMPH
MOVF
TMR1L, W
; Read low byte
MOVWF
TMPL
; Re-enable the Interrupt (if required)
CONTINUE
; Continue with your code
READING A 16-BIT FREE-RUNNING TIMER
; All interrupts are disabled
CLRF
TMR1L
MOVLW
HI_BYTE
MOVWF
TMR1H, F
MOVLW
LO_BYTE
MOVWF
TMR1H, F
; Re-enable the Interrupt (if required)
CONTINUE
; Continue with your code
; Clear Low byte, Ensures no rollover into TMR1H
; Value to load into TMR1H
; Write High byte
; Value to load into TMR1L
; Write Low byte
; Read high byte
; Read low byte
; Read high byte
; Sub 1st read with 2nd read
; Is result = 0
; Good 16-bit read
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