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24AA64 Datasheet(PDF) 5 Page - Microchip Technology |
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24AA64 Datasheet(HTML) 5 Page - Microchip Technology |
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5 / 24 page  2002 Microchip Technology Inc. DS21189F-page 5 24AA64/24LC64 2.0 FUNCTIONAL DESCRIPTION The 24XX64 supports a bi-directional 2-wire bus and data transmission protocol. A device that sends data onto the bus is defined as transmitter, and a device receiving data as receiver. The bus has to be controlled by a master device which generates the serial clock (SCL), controls the bus access and generates the START and STOP conditions, while the 24XX64 works as slave. Both master and slave can operate as trans- mitter or receiver, but the master device determines which mode is activated. 3.0 BUS CHARACTERISTICS The 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 been defined (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 the clock (SCL) is HIGH determines a START condition. All commands must be preceded by a START condition. 3.3 Stop Data Transfer (C) A LOW to HIGH transition of the SDA line while the clock (SCL) is HIGH determines a STOP condition. All operations 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 the duration of the HIGH period of the clock signal. The data on the line must be changed during the LOW period of the clock signal. There is one clock pulse per bit of data. Each data transfer is initiated with a START condition and terminated with a STOP condition. The number of the data bytes transferred between the START and STOP conditions is determined by the master device and is theoretically unlimited, although only the last six- teen will be stored when doing a write operation. When an overwrite does occur it will replace data in a first-in first-out (FIFO) fashion. 3.5 Acknowledge Each receiving device, when addressed, is obliged to generate an acknowledge after the reception of each byte. The master device must generate an extra clock pulse which is associated with this Acknowledge bit. The device that acknowledges, has to pull down the SDA line during the acknowledge clock pulse in such a way that the SDA line is stable LOW during the HIGH period of the acknowledge related clock pulse. Of course, setup and hold times must be taken into account. During reads, a master must signal an end of data to the slave by not generating an Acknowledge bit on the last byte that has been clocked out of the slave. In this case, the slave (24XX64) will leave the data line HIGH to enable the master to generate the STOP con- dition. FIGURE 3-1: DATA TRANSFER SEQUENCE ON THE SERIAL BUS Note: The 24XX64 does not generate any Acknowledge bits if an internal program- ming cycle is in progress. SCL SDA (A) (B) (D) (D) (A) (C) START CONDITION ADDRESS OR ACKNOWLEDGE VALID DATA ALLOWED TO CHANGE STOP CONDITION |
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