11

Atmel AT24CS04/08 [PRELIMINARY DATASHEET]

8766B–SEEPR–8/12

9.

Write Operations

Byte Write: A Byte Write operation requires an 8-bit 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

EEPROM will not respond until the Write is complete (see Figure 10-1 on page 12).

Page Write: The 4-Kbit and 8-Kbit devices are capable of 16-byte Page Writes. A Page Write is initiated in 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 fifteen additional

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 10-2 on page 12).

The data word address lower four 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 internally generated word

address reaches the page boundary, the subsequent byte loaded will be 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 previously loaded

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 next read or write sequence to begin.

10.

Read Operations

Read operations are initiated in the same way as Write operations with the exception that the Read/Write select bit in the

device address word is set to one. There are four types of read operations:



Current Address Read



Random Address Read



Sequential Read



Serial Number Read

Current Address Read: The internal data word address counter maintains the last address accessed during the last

Read or Write operation, incremented by one. This address stays valid between operations as long as the chip power is

maintained. The address roll-over during read is from the last byte of the last memory page to the first byte of the first

page. The address roll-over during write is from the last byte of the current page to the first byte of the same page.

Once the device address with the read/write select bit set to one is clocked in and acknowledged by the EEPROM, the

current address data word is serially clocked out. The microcontroller does not respond with an zero but does generate a

following Stop condition (see Figure 10-3 on page 13).

Random Read: A Random Read requires a dummy byte write sequence to load in the data word address. Once the

device address word and data word address are clocked in and acknowledged by the EEPROM, the microcontroller must

generate another Start condition. The microcontroller now initiates a Current Address Read by sending a device address

with the read/write select bit high. The EEPROM acknowledges the device address and serially clocks out the data word.

The microcontroller does not respond with a zero but does generate a following Stop condition (see Figure 10-4 on page

13).

Sequential Read: Sequential reads are initiated by either a current address read or a random address read. After the

microcontroller receives a data word, it responds with an acknowledge. As long as the EEPROM receives an

acknowledge, it will continue to increment the data word address and serially clock out sequential data words. When the

memory address limit is reached, the data word address will roll-over and the Sequential Read will continue. The

Sequential Read operation is terminated when the microcontroller does not respond with a zero but does generate a

following Stop condition (see Figure 10-5 on page 13).