元器件交易网

Read Operations

Read operations are initiated the same way as write operations with the exception thatthe read/write select bit in the device address word is set to one. There are three readoperations: current address read, random address read and sequential read.

CURRENT ADDRESS READ: The internal data word address counter maintains thelast address accessed during the last read or write operation, incremented by one. Thisaddress stays valid between operations as long as the chip power is maintained. Theaddress “roll over” during read is from the last byte of the last memory page to the firstbyte of the first page. The address “roll over” during write is from the last byte of the cur-rent page to first byte of the same page.

Once the device address with the read/write select bit set to one is clocked in andacknowledged 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 followingstop condition (see Figure 10 on page 11).

RANDOM READ: A random read requires a “dummy” byte write sequence to load in thedata word address. Once the device address word and data word address are clockedin and acknowledged by the EEPROM, the microcontroller must generate another startcondition. The microcontroller now initiates a current address read by sending a deviceaddress with the read/write select bit high. The EEPROM acknowledges the deviceaddress and serially clocks out the data word. The microcontroller does not respondwith a zero but does generate a following stop condition (see Figure 11 on page 11).SEQUENTIAL READ: Sequential reads are initiated by either a current address read ora random address read. After the microcontroller receives a data word, it responds withan acknowledge. As long as the EEPROM receives an acknowledge, it will continue toincrement the data word address and serially clock out sequential data words. When thememory address limit is reached, the data word address will “roll over” and the sequen-tial read will continue. The sequential read operation is terminated when themicrocontroller does not respond with a zero but does generate a following stop condi-tion (see Figure 12 on page 12).Figure 7.

Device Address

10

AT24C164

0105J–SEEPR–12/06