CAT24C256
READ OPERATIOnS
Immediate Address Read
In standby mode, the CAT24C256 internal address
counter points to the data byte immediately following the
last byte accessed by a previous operation. If that ‘previ-
ous’ byte was the last byte in memory, then the address
counter will point to the
st
memory byte, etc.
When, following a START, the CAT24C256 is presented
with a Slave address containing a ‘’ in the R/W bit
position (Figure 8), it will acknowledge (ACK) in the 9
th
clock cycle, and will then transmit data being pointed
at by the internal address counter. The Master can stop
further transmission by issuing a NoACK, followed by a
STOP condition.
Selective Read
The Read operation can also be started at an address
different from the one stored in the internal address
counter. The address counter can be initialized by per-
forming a ‘dummy’ Write operation (Figure 9). Here the
START is followed by the Slave address (with the R/W
bit set to ‘0’) and the desired two byte address. Instead
of following up with data, the Master then issues a 2
nd
START, followed by the ‘Immediate Address Read’ se-
quence, as described earlier.
Sequential Read
If the Master acknowledges the
st
data byte transmitted
by the CAT24C256, then the device will continue trans-
mitting as long as each data byte is acknowledged by
the Master (Figure 0). If the end of memory is reached
during sequential Read, then the address counter will
‘wrap-around’ to the beginning of memory, etc. Sequential
Read works with either ‘Immediate Address Read’ or
‘Selective Read’, the only difference being the starting
byte address.
Doc. No. 04, Rev. D
8
© 2007 by Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
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