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24AA512 Datasheet(PDF) 9 Page - Microchip Technology |
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24AA512 Datasheet(HTML) 9 Page - Microchip Technology |
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9 / 26 page  2004 Microchip Technology Inc. DS21754E-page 9 24AA512/24LC512/24FC512 6.0 WRITE OPERATIONS 6.1 Byte Write Following the Start condition from the master, the control code (four bits), the Chip Select (three bits) and the R/W bit (which is a logic low) are clocked onto the bus by the master transmitter. This indicates to the addressed slave receiver that the address high byte will follow after it has generated an Acknowledge bit during the ninth clock cycle. Therefore, the next byte transmitted by the master is the high-order byte of the word address and will be written into the address pointer of the 24XX512. The next byte is the Least Significant Address byte. After receiving another Acknowledge signal from the 24XX512, the master device will transmit the data word to be written into the addressed memory location. The 24XX512 acknowl- edges again and the master generates a Stop condition. This initiates the internal write cycle and during this time, the 24XX512 will not generate Acknowledge signals (Figure 6-1). If an attempt is made to write to the array with the WP pin held high, the device will acknowledge the command, but no write cycle will occur, no data will be written and the device will immediately accept a new command. After a byte Write command, the internal address counter will point to the address location following the one that was just written. 6.2 Page Write The write control byte, word address and the first data byte are transmitted to the 24XX512 in the same way as in a byte write. But instead of generating a Stop condition, the master transmits up to 127 additional bytes, which are temporarily stored in the on-chip page buffer and will be written into memory after the master has transmitted a Stop condition. After receipt of each word, the seven lower address pointer bits are inter- nally incremented by one. If the master should transmit more than 128 bytes prior to generating the Stop con- dition, the address counter will roll over and the previ- ously received data will be overwritten. As with the byte write operation, once the Stop condition is received, an internal write cycle will begin (Figure 6-2). If an attempt is made to write to the array with the WP pin held high, the device will acknowledge the command, but no write cycle will occur, no data will be written and the device will immediately accept a new command. 6.3 Write Protection The WP pin allows the user to write-protect the entire array (0000-FFFF) when the pin is tied to VCC. If tied to VSS or left floating, the write protection is disabled. The WP pin is sampled at the Stop bit for every Write command (Figure 1-1). Toggling the WP pin after the Stop bit will have no effect on the execution of the write cycle. Note: Page write operations are limited to writing bytes within a single physical page, regardless of the number of bytes actually being written. Physical page boundaries start at addresses that are integer multiples of the page buffer size (or ‘page size’) and end at addresses that are integer multiples of [page size - 1]. If a Page Write command attempts to write across a physical page boundary, the result is that the data wraps around to the beginning of the current page (overwriting data previously stored there), instead of being written to the next page as might be expected. It is therefore necessary for the application software to prevent page write operations that would attempt to cross a page boundary. |
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