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PIC16F627-20/P 参数 Datasheet PDF下载

PIC16F627-20/P图片预览
型号: PIC16F627-20/P
PDF下载: 下载PDF文件 查看货源
内容描述: 基于闪存的8位CMOS微控制器 [FLASH-Based 8-Bit CMOS Microcontrollers]
分类和应用: 闪存微控制器和处理器外围集成电路光电二极管时钟
文件页数/大小: 160 页 / 1657 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC16F62X  
FIGURE 7-2: TIMER1 INCREMENTING EDGE  
T1CKI  
(Default high)  
T1CKI  
(Default low)  
Note: Arrows indicate counter increments.  
7.3  
Timer1 Operation in Asynchronous  
Counter Mode  
EXAMPLE 7-1: READING A 16-BIT  
FREE-RUNNING TIMER  
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 7.3.2).  
; All interrupts are disabled  
MOVF  
MOVWF TMPH  
MOVF TMR1L, W ;Read low byte  
MOVWF TMPL  
MOVF TMR1H, W ;Read high byte  
SUBWF TMPH,  
TMR1H, W ;Read high byte  
;
;
W
;Sub 1st read  
; with 2nd read  
BTFSC STATUS,Z ;Is result = 0  
GOTO CONTINUE ;Good 16-bit read  
In asynchronous counter mode, Timer1 can not be  
used as a time-base for capture or compare operations.  
;
7.3.1  
EXTERNAL CLOCK INPUT TIMING WITH  
UNSYNCHRONIZED CLOCK  
; 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.  
;
If control bit T1SYNC is set, the timer will increment  
completely asynchronously. The input clock must meet  
certain minimum high time and low time requirements.  
Refer to the appropriate Electrical Specifications Sec-  
tion, timing parameters 45, 46, and 47.  
MOVF  
MOVWF TMPH  
MOVF TMR1L, W ;Read low byte  
MOVWF TMPL  
; Re-enable the Interrupt (if required)  
CONTINUE ;Continue with your code  
TMR1H, W ;Read high byte  
;
;
7.3.2  
READING AND WRITING TIMER1 IN  
ASYNCHRONOUS COUNTER MODE  
7.4  
Timer1 Oscillator  
Reading TMR1H or TMR1L while the timer is running,  
from an external asynchronous clock, will guarantee 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.  
A crystal oscillator circuit is built in between pins T1OSI  
(input) and T1OSO (amplifier output). It is enabled by  
setting control bit T1OSCEN (T1CON<3>). The oscilla-  
tor is a low power oscillator rated up to 200 kHz. It will  
continue to run during SLEEP. It is primarily intended  
for a 32 kHz crystal. Table 7-1 shows the capacitor  
selection for the Timer1 oscillator.  
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 unpre-  
dictable value in the timer register.  
The Timer1 oscillator is identical to the LP oscillator.  
The user must provide a software time delay to ensure  
proper oscillator start-up.  
Reading the 16-bit value requires some care.  
Example 7-1 is an example routine to read the 16-bit  
timer value. This is useful if the timer cannot be  
stopped.  
TABLE 7-1:  
CAPACITOR SELECTION FOR  
THE TIMER1 OSCILLATOR  
Osc Type  
Freq  
C1  
C2  
LP  
32 kHz  
100 kHz  
200 kHz  
33 pF  
15 pF  
15 pF  
33 pF  
15 pF  
15 pF  
These values are for design guidance only.  
DS40300B-page 52  
Preliminary  
1999 Microchip Technology Inc.