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2019年11月12日 (火)

2002 Microchip Technology Inc

 7

 24AA64/24LC642.0 FUNCTIONAL DESCRIPTIONThe 24XX64 supports a bi-directional 2-wire bus anddata transmission protocol. A device that sends dataonto the bus is defined as transmitter, and a devicereceiving data as receiver.

  The bus has to be controlledby a master device which generates the serial clock(SCL), controls the bus access and generates theSTART and STOP conditions, while the 24XX64 worksas slave. Both master and slave can operate as trans-mitter or receiver, but the master device determineswhich mode is activated.3.0 BUS CHARACTERISTICSThe following bus protocol has been defined:

  Data transfer may be initiated only when the bus is not busy.

  During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in the data line while the clock line is HIGH will be interpreted as a START or STOP condition.Accordingly, the following bus conditions have beendefined (Figure 3-1).3.1 Bus not Busy (A)Both data and clock lines remain HIGH.3.2 Start Data Transfer (B)A HIGH to LOW transition of the SDA line while theclock (SCL) is HIGH determines a START condition.

  Allcommands must be preceded by a START condition.3.3 Stop Data Transfer (C)A LOW to HIGH transition of the SDA line while theclock (SCL) is HIGH determines a STOP condition. Alloperations must be ended with a STOP condition.3.4 Data Valid (D)The state of the data line represents valid data when,after a START condition, the data line is stable for theduration of the HIGH period of the clock signal.The data on the line must be changed during the LOWperiod of the clock signal.

  There is one clock pulse perbit of data.Each data transfer is initiated with a START conditionand terminated with a STOP condition. The number ofthe data bytes transferred between the START andSTOP conditions is determined by the master deviceand is theoretically unlimited, although only the last six-teen will be stored when doing a write operation. Whenan overwrite does occur it will replace data in a first-infirst-out (FIFO) fashion.

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