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PIC16F877T-20PQ 参数 Datasheet PDF下载

PIC16F877T-20PQ图片预览
型号: PIC16F877T-20PQ
PDF下载: 下载PDF文件 查看货源
内容描述: 8位微控制器\n [8-Bit Microcontroller ]
分类和应用: 微控制器
文件页数/大小: 200 页 / 3338 K
品牌: ETC [ ETC ]
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PIC16F87X  
It may be advantageous to use the high baud rate  
(BRGH = 1) even for slower baud clocks. This is  
because the FOSC/(16(X + 1)) equation can reduce the  
baud rate error in some cases.  
10.1  
USART Baud Rate Generator (BRG)  
The BRG supports both the asynchronous and syn-  
chronous modes of the USART. It is a dedicated 8-bit  
baud rate generator. The SPBRG register controls the  
period of a free running 8-bit timer. In asynchronous  
mode, bit BRGH (TXSTA<2>) also controls the baud  
rate. In synchronous mode, bit BRGH is ignored.  
Table 10-1 shows the formula for computation of the  
baud rate for different USART modes which only apply  
in master mode (internal clock).  
Writing a new value to the SPBRG register causes the  
BRG timer to be reset (or cleared). This ensures the  
BRG does not wait for a timer overflow before output-  
ting the new baud rate.  
10.1.1 SAMPLING  
The data on the RC7/RX/DT pin is sampled three times  
by a majority detect circuit to determine if a high or a  
low level is present at the RX pin.  
Given the desired baud rate and Fosc, the nearest inte-  
ger value for the SPBRG register can be calculated  
using the formula in Table 10-1. From this, the error in  
baud rate can be determined.  
TABLE 10-1: BAUD RATE FORMULA  
SYNC  
BRGH = 0 (Low Speed)  
BRGH = 1 (High Speed)  
0
1
(Asynchronous) Baud Rate = FOSC/(64(X+1))  
(Synchronous) Baud Rate = FOSC/(4(X+1))  
Baud Rate= FOSC/(16(X+1))  
NA  
X = value in SPBRG (0 to 255)  
TABLE 10-2: REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR  
Value on: Value on all  
Address Name  
Bit 7  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1 Bit 0  
POR,  
BOR  
other  
resets  
0000 -010 0000 -010  
0000 000x 0000 000x  
0000 0000 0000 0000  
98h  
18h  
99h  
TXSTA  
CSRC TX9 TXEN SYNC  
BRGH TRMT TX9D  
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D  
SPBRG Baud Rate Generator Register  
Legend: x = unknown, -= unimplemented read as '0'. Shaded cells are not used by the BRG.  
1999 Microchip Technology Inc.  
DS30292B-page 97  
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