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PIC18F4431-I/PT 参数 Datasheet PDF下载

PIC18F4431-I/PT图片预览
型号: PIC18F4431-I/PT
PDF下载: 下载PDF文件 查看货源
内容描述: 28 /40/ 44引脚增强型闪存微控制器采用纳瓦技术,高性能PWM和A / D [28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High-Performance PWM and A/D]
分类和应用: 闪存微控制器
文件页数/大小: 392 页 / 3127 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC18F2331/2431/4331/4431  
REGISTER 3-1:  
OSCTUNE: OSCILLATOR TUNING REGISTER  
U-0  
U-0  
R/W-0  
TUN5  
R/W-0  
TUN4  
R/W-0  
TUN3  
R/W-0  
TUN2  
R/W-0  
TUN1  
R/W-0  
TUN0  
bit 7  
bit 0  
Legend:  
R = Readable bit  
-n = Value at POR  
W = Writable bit  
‘1’ = Bit is set  
U = Unimplemented bit, read as ‘0’  
‘0’ = Bit is cleared x = Bit is unknown  
bit 7-6  
bit 5-0  
Unimplemented: Read as ‘0’  
TUN<5:0>: Frequency Tuning bits  
011111= Maximum frequency  
000001  
000000= Center frequency. Oscillator module is running at the calibrated frequency.  
111111  
100000= Minimum frequency  
3.6.4.1  
Compensating with the EUSART  
3.6.4.3  
Compensating with the CCP Module  
in Capture Mode  
An adjustment may be required when the EUSART  
begins generating framing errors or receives data with  
errors while in Asynchronous mode. Framing errors  
frequently indicate that the device clock frequency is  
too high. To adjust for this, decrement the value in the  
OSCTUNE register to reduce the clock frequency.  
A CCP module can use free-running Timer1 (or  
Timer3), clocked by the internal oscillator block and an  
external event with a known period (such as the AC  
power frequency). The time of the first event is cap-  
tured in the CCPRxH:CCPRxL registers and recorded  
for later use. When the second event causes a capture,  
the time of the first event is subtracted from the time of  
the second event. Since the period of the external  
event is known, the time difference between events can  
be calculated.  
Conversely, errors in data may suggest that the clock  
speed is too low; to compensate, increment the  
OSCTUNE register to increase the clock frequency.  
3.6.4.2  
Compensating with the Timers  
If the measured time is much greater than the calcu-  
lated time, the internal oscillator block is running too  
fast. To compensate for this, decrement the OSCTUNE  
register. If the measured time is much less than the  
calculated time, the internal oscillator block is running  
too slow and the OSCTUNE register should be  
incremented.  
This technique compares the device clock speed to  
that of a reference clock. Two timers may be used: one  
timer clocked by the peripheral clock and the other by  
a fixed reference source, such as the Timer1 oscillator.  
Both timers are cleared, but the timer clocked by the  
reference generates interrupts. When an interrupt  
occurs, the internally clocked timer is read and both  
timers are cleared. If the internally clocked timer value  
is greater than expected, the internal oscillator block is  
running too fast. To adjust for this, decrement the  
OSCTUNE register.  
2010 Microchip Technology Inc.  
DS39616D-page 33  
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