AT21CS01 datasheet(28/47 Pages) MICROCHIP

28 / 47 page

Figure 7-1. Current Address Read

SI/O

MSB

ACK

by Slave

0 A2 A1 A0 1

Device Address

MSB

Data Out Byte (n)

NACK

by Master

Stop Condition

by Master

Start Condition

by Master

7.2

Random Read within the EEPROM

A random read begins in the same way as a byte write operation which will load a new EEPROM memory

address into the Address Pointer. However, instead of sending the data byte and Stop condition of the

byte write, a repeated Start condition is sent to the device. This sequence is referred to as a “dummy

write”. After the device address and memory address bytes of the “dummy write” have been sent, the

AT21CS01/11 will return an ACK response. The master can then initiate a current address read,

beginning with a new Start condition, to read data from the EEPROM. Refer to Current Address Read

within the EEPROM for details on how to perform a current address read.

Figure 7-2. Random Read

SI/O

MSB

ACK

by Slave

0 A2 A1 A0 0

Device Address

Dummy Write

MSB

x A6 A5 A4 A3 A2 A1 A0

Memory Address

MSB

Data Out Byte (n)

ACK

by Slave

NACK

by Master

Stop Condition

by Master

Start Condition

by Master

MSB

ACK

by Slave

0 A2 A1 A0 1

Device Address

Restart

by Master

7.3

Sequential Read within the EEPROM

Sequential reads start as either a current address read or as a random read. However, instead of the

master sending a NACK (logic ‘1’) response to end a read operation after a single byte of data has been

read, the master sends an ACK (logic ‘0’) to instruct the AT21CS01/11 to output another byte of data. As

long as the device receives an ACK from the master after each byte of data has been output, it will

continue to increment the address counter and output the next byte data from the EEPROM. If the end of

the EEPROM is reached, then the Address Pointer will “roll over” back to the beginning (address 00h) of

the EEPROM region. To end the sequential read operation, the master must send a NACK response after

the device has output a complete byte of data. After the device receives the NACK, it will end the read

operation and return to the Standby mode.

Note:

If the last operation to the device accessed the Security register, then a random read should be

performed to ensure that the Address Pointer is set to a known memory location within the

EEPROM.

Figure 7-3. Sequential Read from a Current Address Read

SI/O

MSB

ACK

by Slave

0 A2 A1 A0 1

Device Address

MSB

Data Out Byte (n)

ACK

by Master

MSB

Data Out Byte (n+x)

NACK

by Master

Stop Conditon

by Master

Start Condition

by Master

AT21CS01/AT21CS11

Datasheet

DS20005857A-page 28

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