The I2" />
參數(shù)資料
型號: PIC18F452-I/PT
廠商: Microchip Technology
文件頁數(shù): 105/134頁
文件大小: 0K
描述: IC MCU FLASH 16KX16 EE 44TQFP
產(chǎn)品培訓(xùn)模塊: Asynchronous Stimulus
8-bit PIC® Microcontroller Portfolio
標準包裝: 160
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,LVD,POR,PWM,WDT
輸入/輸出數(shù): 34
程序存儲器容量: 32KB(16K x 16)
程序存儲器類型: 閃存
EEPROM 大?。?/td> 256 x 8
RAM 容量: 1.5K x 8
電壓 - 電源 (Vcc/Vdd): 4.2 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 8x10b
振蕩器型: 外部
工作溫度: -40°C ~ 85°C
封裝/外殼: 44-TQFP
包裝: 托盤
配用: XLT44PT3-ND - SOCKET TRAN ICE 44MQFP/TQFP
AC164305-ND - MODULE SKT FOR PM3 44TQFP
444-1001-ND - DEMO BOARD FOR PICMICRO MCU
AC164020-ND - MODULE SKT PROMATEII 44TQFP
PIC16C9XX
DS30444E - page 72
1997 Microchip Technology Inc.
11.2.4
MULTI-MASTER
The I2C protocol allows a system to have more than
one master. This is called multi-master. When two or
more masters try to transfer data at the same time, arbi-
tration and synchronization occur.
11.2.4.1
ARBITRATION
Arbitration takes place on the SDA line, while the SCL
line is high. The master which transmits a high when the
other
master
transmits
a
low
loses
arbitration
(Figure 11-16), and turns off its data output stage. A
master which lost arbitration can generate clock pulses
until the end of the data byte where it lost arbitration.
When the master devices are addressing the same
device, arbitration continues into the data.
FIGURE 11-16: MULTI-MASTER
ARBITRATION
(TWO MASTERS)
Masters that also incorporate the slave function, and
have lost arbitration must immediately switch over to
slave-receiver mode. This is because the winning mas-
ter-transmitter may be addressing it.
Arbitration is not allowed between:
A repeated START condition
A STOP condition and a data bit
A repeated START condition and a STOP condi-
tion
Care needs to be taken to ensure that these conditions
do not occur.
transmitter 1 loses arbitration
DATA 1 SDA
DATA 1
DATA 2
SDA
SCL
11.2.4.2 Clock Synchronization
Clock synchronization occurs after the devices have
started
arbitration. This
is
performed
using
a
wired-AND connection to the SCL line. A high to low
transition on the SCL line causes the concerned
devices to start counting off their low period. Once a
device clock has gone low, it will hold the SCL line low
until its SCL high state is reached. The low to high tran-
sition of this clock may not change the state of the SCL
line, if another device clock is still within its low period.
The SCL line is held low by the device with the longest
low period. Devices with shorter low periods enter a
high wait-state, until the SCL line comes high. When the
SCL line comes high, all devices start counting off their
high periods. The rst device to complete its high period
will pull the SCL line low. The SCL line high time is
determined by the device with the shortest high period,
FIGURE 11-17: CLOCK SYNCHRONIZATION
CLK
1
CLK
2
SCL
wait
state
start counting
HIGH period
counter
reset
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