AT24C64D-XHM データシートの表示（PDF） - Atmel Corporation

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AT24C64D-XHM

2-Wire Serial Electrically Erasable and Programmable Read-only Memory

Atmel Corporation 

Atmel AT24C32D/64D

5. Device Addressing

The 32K/64K EEPROM requires an 8-bit device address word following a start condition to enable the chip for a

read or write operation (see Figure 7-1 on page 10 ). The device address word consists of a mandatory one, zero

sequence for the first four most significant bits as shown. This is common to all 2-wire EEPROM devices.

The 32K/64K uses the three device address bits A2, A1, A0 to allow as many as eight devices on the same bus.

These bits must compare to their corresponding hardwired input pins. The A2, A1, and A0 pins use an internal

proprietary circuit that biases them to a logic low condition if the pins are allowed to float.

The eighth bit of the device address is the read/write operation 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 device will

return to standby state.

DATA SECURITY: The Atmel® AT24C32D/64D has a hardware data protection scheme that allows the user to

write protect the entire memory when the WP pin is at VCC.

6. Write Operations

BYTE WRITE: A write operation requires two 8-bit data word addresses 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, tWR, to the nonvolatile memory. All inputs are disabled during this

write cycle and the EEPROM will not respond until the write is complete (see Figure 7-2 on page 10).

PAGE WRITE: The 32K/64K EEPROM is capable of 32-byte page writes.

A page write is initiated the same way 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

microcontroller can transmit up to 31 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 (see Figure 7-3 on

page 11).

The data word address lower five bits are internally incremented 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, internally generated, reaches the page boundary, the following byte is placed at the beginning of the

same page. If more than 32 data words are transmitted to the EEPROM, the data word address will “roll over” and

previous data will be overwritten.

ACKNOWLEDGE POLLING: Once the internally-timed write cycle has started and the EEPROM inputs are

disabled, 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.

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8717B–SEEPR–6/10

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