參數(shù)資料
型號: PIC18F4420-I/ML
廠商: Microchip Technology
文件頁數(shù): 63/151頁
文件大?。?/td> 0K
描述: IC MCU FLASH 8KX16 44QFN
產(chǎn)品培訓(xùn)模塊: Asynchronous Stimulus
8-bit PIC® Microcontroller Portfolio
標(biāo)準(zhǔn)包裝: 45
系列: PIC® 18F
核心處理器: PIC
芯體尺寸: 8-位
速度: 40MHz
連通性: I²C,SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,HLVD,POR,PWM,WDT
輸入/輸出數(shù): 36
程序存儲器容量: 16KB(8K x 16)
程序存儲器類型: 閃存
EEPROM 大?。?/td> 256 x 8
RAM 容量: 768 x 8
電壓 - 電源 (Vcc/Vdd): 4.2 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 13x10b
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 44-VQFN 裸露焊盤
包裝: 管件
產(chǎn)品目錄頁面: 643 (CN2011-ZH PDF)
配用: XLT44QFN2-ND - SOCKET TRAN ICE 44QFN/40DIP
AC164322-ND - MODULE SOCKET MPLAB PM3 28/44QFN
444-1001-ND - DEMO BOARD FOR PICMICRO MCU
PIC16(L)F1782/3
DS41579C-page 330
Preliminary
2011-2012 Microchip Technology Inc.
27.4
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 BAUDCON register selects 16-bit
mode.
The SPBRGH, SPBRGL 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 BAUDCON register. In
Synchronous mode, the BRGH bit is ignored.
Table 27-3 contains the formulas for determining the
baud rate. Example 27-1 provides a sample calculation
for determining the baud rate and baud rate error.
Typical baud rates and error values for various
asynchronous modes have been computed for your
convenience and are shown in Table 27-3. 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.
Writing a new value to the SPBRGH, SPBRGL 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.
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.
EXAMPLE 27-1:
CALCULATING BAUD
RATE ERROR
For a device with FOSC of 16 MHz, desired baud rate
of 9600, Asynchronous mode, 8-bit BRG:
Solving for SPBRGH:SPBRGL:
X
FOSC
Desired Baud Rate
---------------------------------------------
64
--------------------------------------------- 1
=
Desired Baud Rate
FOSC
64 [SPBRGH:SPBRGL]
1
+
------------------------------------------------------------------------
=
16000000
9600
------------------------
64
------------------------1
=
25.042
25
==
Calculated Baud Rate
16000000
64 25
1
+
---------------------------
=
9615
=
Error
Calc. Baud Rate Desired Baud Rate
Desired Baud Rate
--------------------------------------------------------------------------------------------
=
9615 9600
9600
----------------------------------
0.16%
==
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