16K I2C Serial EEPROM - Hifi-remote.com

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24AA16/24LC16B3.6 Device AddressingA control byte is the first byte received following thestart condition from the master device. The control byteconsists of a four bit control code, for the 24XX16 thisis set as 1010 binary for read and write operations.The next three bits of the control byte are the blockselect bits (B2, B1, B0). They are used by the masterdevice to select which of the eight 256 word blocks ofmemory are to be accessed. These bits are in effect thethree most significant bits of the word address. Itshould be noted that the protocol limits the size of thememory to eight blocks of 256 words, therefore the protocolcan support only one 24XX16 per system.The last bit of the control byte defines the operation tobe performed. When set to ‘1’ a read operation isselected, when set to ‘0’ a write operation is selected.Following the START condition, the 24XX16 monitorsthe SDA bus checking the device type identifier beingtransmitted, upon a 1010 code the slave device outputsan acknowledge signal on the SDA line. Dependingon the state of the R/W bit, the 24XX16 will select aread or write operation.OperationControlCodeBlock SelectR/WRead 1010 Block Address 1Write 1010 Block Address 0FIGURE 3-2:STARTCONTROL BYTEALLOCATIONSLAVE ADDRESSREAD/WRITER/W1 0 1 0 B2 B1 B0ADS21703B-page 6© 2002 Microchip Technology Inc.
24AA16/24LC16B4.0 WRITE OPERATION4.1 Byte WriteFollowing the START condition from the master, thedevice code (4 bits), the block address (3 bits) and theR/W bit which is a logic LOW is placed onto the bus bythe master transmitter. This indicates to the addressedslave receiver that a byte with a word address will followafter it has generated an acknowledge bit duringthe ninth clock cycle. Therefore, the next byte transmittedby the master is the word address and will be writteninto the address pointer of the 24XX16. Afterreceiving another acknowledge signal from the24XX16, the master device will transmit the data wordto be written into the addressed memory location. The24XX16 acknowledges again and the master generatesa STOP condition. This initiates the internal writecycle, and during this time the 24XX16 will not generateacknowledge signals (Figure 4-1).4.2 Page WriteThe write control byte, word address and the first databyte are transmitted to the 24XX16 in the same way asin a byte write. But instead of generating a STOP conditionthe master transmits up to 16 data bytes to the24XX16, which are temporarily stored in the on-chippage buffer and will be written into the memory after themaster has transmitted a STOP condition. After thereceipt of each word, the four lower order addresspointer bits are internally incremented by ‘1’. Thehigher order 7 bits of the word address remains constant.If the master should transmit more than 16 wordsprior to generating the STOP condition, the addresscounter will roll over and the previously received datawill be overwritten. As with the byte write operation,once the STOP condition is received an internal writecycle will begin (Figure 4-2).Note:Page write operations are limited to writingbytes within a single physical page,regardless of the number of bytes actuallybeing written. Physical page boundariesstart at addresses that are integermultiples of the page buffer size (or‘page size’) and end at addresses thatare integer multiples of [page size - 1]. Ifa page write <strong>com</strong>mand attempts to writeacross a physical page boundary, theresult is that the data wraps around tothe beginning of the current page (overwritingdata previously stored there),instead of being written to the next pageas might be expected. It is thereforenecessary for the application software toprevent page write operations thatwould attempt to cross a page boundary.FIGURE 4-1:BYTE WRITEBUS ACTIVITYMASTERSTARTCONTROLBYTEWORDADDRESSDATASTOPSDA LINESPBUS ACTIVITYACKACKACKFIGURE 4-2:PAGE WRITEBUS ACTIVITYMASTERSTARTCONTROLBYTEWORDADDRESS (n) DATA (n) DATA (n + 1) DATA (n + 15)STOPSDA LINEBUS ACTIVITYSACKACKACKACKACKP© 2002 Microchip Technology Inc. DS21703B-page 7
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16K I2C Serial EEPROM - Hifi-remote.com

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