CAT24WC128
Preliminary
protected and becomes read only. The CAT24WC128
will accept both slave and byte addresses, but the
memory location accessed is protected from program-
ming by the device’s failure to send an acknowledge
after the first byte of data is received.
acknowledge, and internally increment the six low order
address bits by one. The high order bits remain un-
changed.
IftheMastertransmitsmorethan64bytesbeforesending
the STOP condition, the address counter ‘wraps around’,
and previously transmitted data will be overwritten.
READ OPERATIONS
When all 64 bytes are received, and the STOP condition
has been sent by the Master, the internal programming
cycle begins. At this point, all received data is written to
the CAT24WC128 in a single write cycle.
The READ operation for the CAT24WC128 is initiated in
the same manner as the write operation with one excep-
tion, that R/W bit is set to one. Three different READ
operations are possible: Immediate/Current Address
READ,Selective/RandomREADandSequentialREAD.
Acknowledge Polling
Disabling of the inputs can be used to take advantage of
the typical write cycle time. Once the stop condition is
issued to indicate the end of the host's write operation,
CAT24WC128 initiates the internal write cycle. ACK
polling can be initiated immediately. This involves issu-
ing the start condition followed by the slave address for
a write operation. If CAT24WC128 is still busy with the
write operation, no ACK will be returned. If
CAT24WC128 has completed the write operation, an
ACK will be returned and the host can then proceed with
the next read or write operation.
Immediate/Current Address Read
The CAT24WC128’s address counter contains the ad-
dress of the last byte accessed, incremented by one. In
other words, if the last READ or WRITE access was to
address N, the READ immediately following would ac-
cess data from address N+1. If N=E (where E=16383),
then the counter will ‘wrap around’ to address 0 and
continue to clock out data. After the CAT24WC128
receives its slave address information (with the R/W bit
set to one), it issues an acknowledge, then transmits the
8 bit byte requested. The master device does not send
an acknowledge, but will generate a STOP condition.
WRITE PROTECTION
Selective/Random Read
The Write Protection feature allows the user to protect
against inadvertent programming of the memory array.
If the WP pin is tied to VCC, the entire memory array is
Selective/Random READ operations allow the Master
device to select at random any memory location for a
Figure 6. Byte Write Timing
S
T
A
R
T
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
BYTE ADDRESS
–A A –A
0
A
DATA
15
8
7
SDA LINE
S
P
*
*
A
C
K
A
C
K
A
C
K
A
C
K
24WC128 F08
*=Don't Care Bit
Figure 7. Page Write Timing
S
T
A
R
T
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
BYTE ADDRESS
–A A –A
0
A
DATA
DATA n
DATA n+63
15
8
7
SDA LINE
S
P
*
*
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
24WC128 F09
*=Don't Care Bit
Doc. No. 25060-00 6/99 S-1
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CATALYST [ CATALYST SEMICONDUCTOR ]
