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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  
12.1  
USART Baud Rate Generator (BRG)  
EXAMPLE 12-1: CALCULATING BAUD RATE  
ERROR  
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 12-1 shows the formula for computation of the  
baud rate for different USART modes which only apply  
in master mode (internal clock).  
Desired Baud rate = Fosc / (64 (X + 1))  
9600 =  
16000000 /(64 (X + 1))  
X
=
Î25.042° = 25  
Calculated Baud Rate=16000000 / (64 (25 + 1))  
=
=
9615  
Error  
(Calculated Baud Rate - Desired Baud Rate)  
Desired Baud Rate  
Given the desired baud rate and Fosc, the nearest inte-  
ger value for the SPBRG register can be calculated  
using the formula in Table 12-1. From this, the error in  
baud rate can be determined.  
=
=
(9615 - 9600) / 9600  
0.16%  
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.  
Example 12-1 shows the calculation of the baud rate  
error for the following conditions:  
FOSC = 16 MHz  
Desired Baud Rate = 9600  
BRGH = 0  
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.  
SYNC = 0  
TABLE 12-1: 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 12-2: REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR  
Value on Value on all  
POR other resets  
Address Name  
Bit 7  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Bit 0  
0000 -010 0000 -010  
98h  
TXSTA  
CSRC TX9 TXEN SYNC  
BRGH TRMT TX9D  
0000 -00x 0000 -00x  
0000 0000 0000 0000  
18h  
99h  
RCSTA SPEN RX9 SREN CREN ADEN 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.  
Preliminary  
DS40300B-page 73