CAT24C03, CAT24C05
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8
READ OPERATIONS
Immediate Read
Upon receiving a Slave address with the R/W bit set to ‘1’,
the CAT24C03/05 will interpret this as a request for data
residing at the current byte address in memory. The
CAT24C03/05 will acknowledge the Slave address, will
immediately shift out the data residing at the current address,
and will then wait for the Master to respond. If the Master
does not acknowledge the data (NoACK) and then follows
up with a STOP condition (Figure 10), the CAT24C03/05
returns to Standby mode.
Selective Read
Selective Read operations allow the Master device to
select at random any memory location for a read operation.
The Master device first performs a ‘dummy’ write operation
by sending the START condition, slave address and byte
address of the location it wishes to read. After the
CAT24C03/05 acknowledges the byte address, the Master
device resends the START condition and the slave address,
this time with the R/W
bit set to one. The CAT24C03/05 then
responds with its acknowledge and sends the requested data
byte. The Master device does not acknowledge the data
(NoACK) but will generate a STOP condition (Figure 11).
Sequential Read
If during a Read session, the Master acknowledges the 1
st
data byte, then the CAT24C03/05 will continue transmitting
data residing at subsequent locations until the Master
responds with a NoACK, followed by a STOP (Figure 12).
In contrast to Page Write, during Sequential Read the
address count will automatically increment to and then
wrapïaround at end of memory (rather than end of page).
SCL
SDA 8
th
Bit
STOPNO ACKDATA OUT
89
SLAVE
ADDRESS
S
A
C
K
DATA
BYTE
N
O
A
C
K
S
T
O
P
P
S
T
A
R
T
BUS ACTIVITY:
MASTER
SLAVE
Figure 10. Immediate Read Sequence and Timing
SLAVE
S
A
C
K
N
O
A
C
K
S
T
O
P
P
S
T
A
R
T
S
A
C
K
SLAVE
ADDRESS
A
C
K
S
T
A
R
T
DATA
BYTE
ADDRESS
BYTEADDRESS
BUS ACTIVITY:
MASTER
SLAVE
Figure 11. Selective Read Sequence
S
T
O
P
P
SLAVE
ADDRESS
A
C
K
A
C
K
A
C
K
N
O
A
C
K
A
C
K
DATA
BYTE
n
DATA
BYTE
n+1
DATA
BYTE
n+2
DATA
BYTE
n+x
BUS ACTIVITY:
MASTER
SLAVE
Figure 12. Sequential Read Sequence
