FT24C512/A
DS3009E-page6 © 2009 Fremont Micro Devices Inc.
READ OPERATIONS
The read command is similar to the write command except the 8
th
read/write bit in address word is set to
“1”. The three read operation modes are described as follows:
(A) CURRENT ADDRESS READ
The EEPROM internal address word counter maintains the last read or write address plus one if the
power supply to the device has not been cut off. To initiate a current address read operation, the
micro-controller issues a START bit and a valid device address word with the read/write bit (8
th
) set to
“1”. The EEPROM will response with an ACKNOWLEDGE signal on the 9
th
serial clock cycle. An 8-
bit data word will then be serially clocked out. The internal address word counter will then
automatically increase by one. For current address read the micro-controller will not issue an
ACKNOWLEDGE signal on the 18
th
clock cycle. The micro-controller issues a valid STOP bit after
the 18
th
clock cycle to terminate the read operation. The device then returns to STANDBY mode (see
Figure 7).
(B) SEQUENTIAL READ
The sequential read is very similar to current address read. The micro-controller issues a START bit
and a valid device address word with read/write bit (8
th
) set to “1”. The EEPROM will response with
an ACKNOWLEDGE signal on the 9
th
serial clock cycle. An 8-bit data word will then be serially
clocked out. Meanwhile the internally address word counter will then automatically increase by one.
Unlike current address read, the micro-controller sends an ACKNOWLEDGE signal on the 18th clock
cycle signaling the EEPROM device that it wants another byte of data. Upon receiving the
ACKNOWLEDGE signal, the EEPROM will serially clocked out an 8-bit data word based on the
incremented internal address counter. If the micro-controller needs another data, it sends out an
ACKNOWLEDGE signal on the 27
th
clock cycle. Another 8-bit data word will then be serially clocked
out. This sequential read continues as long as the micro-controller sends an ACKNOWLEDGE signal
after receiving a new data word. When the internal address counter reaches its maximum valid
address, it rolls over to the beginning of the memory array address. Similar to current address read,
the micro-controller can terminate the sequential read by not acknowledging the last data word
received, but sending a STOP bit afterwards instead (figure 8).
(C) RANDOM READ
Random read is a two-steps process. The first step is to initialize the internal address counter with a
target read address using a “dummy write” instruction. The second step is a current address read.
To initialize the internal address counter with a target read address, the micro-controller issues a
START bit first, follows by a valid device address with the read/write bit (8
th
) set to “0”. The EEPROM
will then acknowledge. The micro-controller will then send two address words. Again the EEPROM
will acknowledge. Instead of sending a valid written data to the EEPROM, the micro-controller
performs a current address read instruction to read the data. Note that once a START bit is issued,
the EEPROM will reset the internal programming process and continue to execute the new instruction
- which is to read the current address (figure 9).
