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AT34C02-10PI Datasheet(PDF) 7 Page - ATMEL Corporation |
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AT34C02-10PI Datasheet(HTML) 7 Page - ATMEL Corporation |
7 / 12 page AT34C02 7 Device Addressing The 2K EEPROM device requires an 8-bit device address word following a start condition to enable the chip for a read or write operation (refer to Figure 2). The device address word consists of a mandatory one-zero sequence for the first four most-significant bits (1010) for normal read and write operations and 0110 for writing to the write protect register. The next 3 bits are the A2, A1 and A0 device address bits for the AT34C02 EEPROM. These 3 bits must compare to their corresponding hard-wired input pins. The eighth bit of the device address is the read/write opera- tion select bit. A read operation is initiated if this bit is high and a write operation is initiated if this bit is low. Upon a compare of the device address, the EEPROM will output a zero. If a compare is not made, the chip will return to a standby state. The device will not acknowledge if the write protect register has been programmed and the control code is 0110. Write Operations BYTE WRITE: A write operation requires an 8-bit data word address following the device address word and acknowledgment. Upon receipt of this address, the EEPROM will again respond with a zero and then clock in the first 8-bit data word. Following receipt of the 8-bit data word, the EEPROM will output a zero and the addressing device, such as a microcontroller, must terminate the write sequence with a stop condition. At this time the EEPROM enters an internally-timed write cycle, t WR, to the nonvolatile memory. All inputs are disabled during this write cycle and the EEPROM will not respond until the write is complete (refer to Figure 3). The device will acknowledge a write command, but not write the data, if the software or hardware write protection has been enabled. The write cycle time must be observed even when the write protection is enabled. PAGE WRITE: The 2K device is capable of 16-byte page write. A page write is initiated the same as a byte write, but the microcontroller does not send a stop condition after the first data word is clocked in. Instead, after the EEPROM acknowledges receipt of the first data word, the microcon- troller can transmit up to fifteen more data words. The EEPROM will respond with a zero after each data word received. The microcontroller must terminate the page write sequence with a stop condition (refer to Figure 4). The data word address lower four bits are internally incre- mented following the receipt of each data word. The higher data word address bits are not incremented, retaining the memory page row location. When the word address, inter- nally generated, reaches the page boundary, the following byte is placed at the beginning of the same page. If more than sixteen data words are transmitted to the EEPROM, the data word address will “roll over” and previous data will be overwritten. The address “roll over” during write is from the last byte of the current page to the first byte of the same page. The device will acknowledge a write command, but not write the data, if the software or hardware write protection has been enabled. The write cycle time must be observed even when the write protection is enabled. ACKNOWLEDGE POLLING: Once the internally-timed write cycle has started and the EEPROM inputs are dis- abled, acknowledge polling can be initiated. This involves sending a start condition followed by the device address word. The read/write bit is representative of the operation desired. Only if the internal write cycle has completed will the EEPROM respond with a zero allowing the read or write sequence to continue. Write Protection The software write protection, once enabled, permanently write protects only the first-half of the array (00H - 7FH) while the hardware write protection, via the WP pin, is used to protect the entire array. SOFTWARE WRITE PROTECTION: The software write protection is enabled by sending a command, similar to a normal write command, to the device which programs the write protect register. This must be done with the WP pin low. The write protect register is programmed by sending a write command with the device address of 0110 instead of 1010 with the address and data bit being don’t cares (refer to Figure 1). Once the software write protection has been enabled, the device will no longer acknowledge the 0110 control byte. The software write protection cannot be reversed even if the device is powered down. The write cycle time must be observed. HARDWARE WRITE PROTECTION: The WP pin can be connected to V CC, GND, or left floating. Connecting the WP pin to V CC will write protect the entire array, regardless of whether or not the software write protection has been enabled. The software write protection register cannot be programmed when the WP pin is connected to V CC. If the WP pin is connected to GND or left floating, the write pro- tection mode is determined by the status of the software write protect register. |
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