Read
Operations
Read operations are initiated 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 three read operations:
current address read, random address read and sequential 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 “rollover”
during read is from the last byte of the last memory page, to the first byte of the first page.
Once the device address with the read/write select bit set to one is clocked in and acknowl-
edged by the EEPROM, the current address data word is serially clocked out. The
microcontroller does not respond with an input zero but does generate a following stop condi-
tion (refer to Figure 4).
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 fol-
lowing stop condition (refer to Figure 5).
SEQUENTIAL READ: Sequential reads are initiated by either a current address read or a ran-
dom 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 con-
tinue. The sequential read operation is terminated when the microcontroller does not respond
with a zero, but does generate a following stop condition (refer to Figure 6).
10
AT24C1024
1471H–SEEPR–03/03
ATMEL [ ATMEL ]
