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PIC16F688-I/ST 参数 Datasheet PDF下载

PIC16F688-I/ST图片预览
型号: PIC16F688-I/ST
PDF下载: 下载PDF文件 查看货源
内容描述: 14引脚基于闪存的8位CMOS微控制器采用纳瓦技术 [14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology]
分类和应用: 闪存微控制器
文件页数/大小: 202 页 / 3832 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC16F688  
If the system clock is changed during an active receive  
operation, a receive error or data loss may result. To  
avoid this problem, check the status of the RCIDL bit to  
make sure that the receive operation is Idle before  
changing the system clock.  
10.3 EUSART Baud Rate Generator  
(BRG)  
The Baud Rate Generator (BRG) is an 8-bit or 16-bit  
timer that is dedicated to the support of both the  
asynchronous and synchronous EUSART operation.  
By default, the BRG operates in 8-bit mode. Setting the  
BRG16 bit of the BAUDCTL register selects 16-bit  
mode.  
EXAMPLE 10-1:  
CALCULATING BAUD  
RATE ERROR  
For a device with FOSC of 16 MHz, desired baud rate  
of 9600, Asynchronous mode, 8-bit BRG:  
The SPBRGH, SPBRG register pair determines the  
period of the free running baud rate timer. In  
Asynchronous mode the multiplier of the baud rate  
period is determined by both the BRGH bit of the TXSTA  
register and the BRG16 bit of the BAUDCTL register. In  
Synchronous mode, the BRGH bit is ignored.  
FOSC  
--------------------------------------------------------------------  
=
Desired Baud Rate  
64([SPBRGH:SPBRG] + 1)  
Solving for SPBRGH:SPBRG:  
FOSC  
---------------------------------------------  
Table 10-3 contains the formulas for determining the  
baud rate. Example 10-1 provides a sample calculation  
for determining the baud rate and baud rate error.  
Desired Baud Rate  
---------------------------------------------  
X =  
=
1  
64  
16000000  
-----------------------  
9600  
64  
Typical baud rates and error values for various  
asynchronous modes have been computed for your  
convenience and are shown in Table 10-3. It may be  
advantageous to use the high baud rate (BRGH = 1),  
or the 16-bit BRG (BRG16 = 1) to reduce the baud rate  
error. The 16-bit BRG mode is used to achieve slow  
baud rates for fast oscillator frequencies.  
-----------------------  
1  
= [25.042] = 25  
16000000  
64(25 + 1)  
--------------------------  
=
Calculated Baud Rate  
= 9615  
Writing a new value to the SPBRGH, SPBRG register  
pair causes the BRG timer to be reset (or cleared). This  
ensures that the BRG does not wait for a timer overflow  
before outputting the new baud rate.  
Calc. Baud Rate Desired Baud Rate  
--------------------------------------------------------------------------------------------  
Error =  
Desired Baud Rate  
(9615 9600)  
----------------------------------  
=
= 0.16%  
9600  
TABLE 10-3: BAUD RATE FORMULAS  
Configuration Bits  
Baud Rate Formula  
BRG/EUSART Mode  
SYNC  
BRG16  
BRGH  
0
0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
x
x
8-bit/Asynchronous  
8-bit/Asynchronous  
16-bit/Asynchronous  
16-bit/Asynchronous  
8-bit/Synchronous  
16-bit/Synchronous  
FOSC/[64 (n+1)]  
FOSC/[16 (n+1)]  
FOSC/[4 (n+1)]  
Legend:  
x= Don’t care, n = value of SPBRGH, SPBRG register pair  
TABLE 10-4: REGISTERS ASSOCIATED WITH THE BAUD RATE GENERATOR  
Value on  
all other  
Resets  
Value on  
POR, BOR  
Name  
Bit 7  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Bit 0  
BAUDCTL ABDOVF RCIDL  
SCKP  
CREN  
BRG4  
BRG12  
SYNC  
BRG16  
ADDEN  
BRG3  
WUE  
OERR  
BRG1  
BRG9  
TRMT  
ABDEN 01-0 0-00 01-0 0-00  
RCSTA  
SPBRG  
SPBRGH  
TXSTA  
SPEN  
BRG7  
BRG15  
CSRC  
RX9  
BRG6  
BRG14  
TX9  
SREN  
BRG5  
BRG13  
TXEN  
FERR  
BRG2  
BRG10  
BRGH  
RX9D  
BRG0  
BRG8  
TX9D  
0000 000x 0000 000x  
0000 0000 0000 0000  
0000 0000 0000 0000  
0000 0010 0000 0010  
BRG11  
SENDB  
Legend:  
x= unknown, – = unimplemented read as ‘0’. Shaded cells are not used for the Baud Rate Generator.  
© 2007 Microchip Technology Inc.  
DS41203D-page 95  
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