CAT24C64
READ OPERATIONS
Immediate Read
Write sequence by sending data, the Master then creates a
START condition and broadcasts a Slave address with the
R/W bit set to ‘1’. The Slave responds with ACK after every
byte sent by the Master and then sends out data residing at
the selected address. After receiving the data, the Master
responds with NoACK and then terminates the session by
creating a STOP condition on the bus (Figure 11).
To read data from memory, the Master creates a START
condition on the bus and then broadcasts a Slave address
with the R/W bit set to ‘1’. The Slave responds with ACK
and starts shifting out data residing at the current address.
After receiving the data, the Master responds with NoACK
and terminates the session by creating a STOP condition on
the bus (Figure 10). The Slave then returns to Standby mode.
Sequential Read
Selective Read
If, after receiving data sent by the Slave, the Master
responds with ACK, then the Slave will continue
transmitting until the Master responds with NoACK
followed by STOP (Figure 12). During Sequential Read the
internal byte address is automatically incremented up to the
end of memory, where it then wraps around to the beginning
of memory.
To read data residing at a specific address, the selected
address must first be loaded into the internal address register.
This is done by starting a Byte Write sequence, whereby the
Master creates a START condition, then broadcasts a Slave
address with the R/W bit set to ‘0’ and then sends two
address bytes to the Slave. Rather than completing the Byte
N
S
T
A
R
T
O
BUS ACTIVITY:
MASTER
S
A T
C O
K P
SLAVE
ADDRESS
S
P
A
DATA
C
SLAVE
8
BYTE
K
SCL
SDA
9
8th Bit
DATA OUT
NO ACK
STOP
Figure 10. Immediate Read Sequence and Timing
N
O
A
C
K
BUS ACTIVITY:
S
T
A
R
T
S
T
A
S
T
ADDRESS
BYTE
ADDRESS
BYTE
SLAVE
SLAVE
MASTER
R
T
O
P
ADDRESS
ADDRESS
S
S
P
A
C
K
A
C
K
A
C
K
A
C
K
SLAVE
DATA
BYTE
Figure 11. Selective Read Sequence
N
O
A
C
K
BUS ACTIVITY:
MASTER
S
T
A
C
K
A
C
K
A
C
K
SLAVE
ADDRESS
O
P
P
A
C
K
SLAVE
DATA
BYTE
n
DATA
BYTE
n+1
DATA
BYTE
n+2
DATA
BYTE
n+x
Figure 12. Sequential Read Sequence
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