X4643 Datasheet, PDF (9/21 Pages) Xicor Inc. – CPU Supervisor with 64K EEPROM

X4643, X4645
Serial Write Operations
BYTE WRITE
For a write operation, the device requires the Slave
Address Byte and a Word Address Byte. This gives the
master access to any one of the words in the array.
After receipt of the Word Address Byte, the device
responds with an acknowledge, and awaits the next
eight bits of data. After receiving the 8 bits of the Data
Byte, the device again responds with an acknowledge.
The master then terminates the transfer by generating a
stop condition, at which time the device begins the inter-
nal write cycle to the nonvolatile memory. During this
internal write cycle, the device inputs are disabled, so the
device will not respond to any requests from the master.
The SDA output is at high impedance. See Figure 8.
Figure 8. Byte Write Sequence
Signals from
S
the Master
t
a ^Slave
r
Word Address Word Address
Byte 1
Byte 0
Data
S
t
o
SDA Bus
10 1 0
0
Signals from
A
the Slave
C
K
A write to a protected block of memory will suppress
the acknowledge bit.
Page Write
The device is capable of a page write operation. It is
initiated in the same manner as the byte write opera-
tion; but instead of terminating the write cycle after the
first data byte is transferred, the master can transmit
an unlimited number of 8-bit bytes. After the receipt of
each byte, the device will respond with an acknowl-
edge, and the address is internally incremented by
one. The page address remains constant. When the
A
A
A
C
C
C
K
K
K
counter reaches the end of the page, it “rolls over” and
goes back to ‘0’ on the same page. This means that
the master can write 64-bytes to the page starting at
any location on that page. If the master begins writing
at location 60, and loads 12-bytes, then the first 4-
bytes are written to locations 60 through 63, and the
last 8-bytes are written to locations 0 through 7. After-
wards, the address counter would point to location 8 of
the page that was just written. If the master supplies
more than 64-bytes of data, then new data over-writes
the previous data, one byte at a time.
Figure 9. Page Write Operation
S
Signals from _t
the Master _a
r
Slave
Word Ad-
Word Ad-
(1 < n < 64)
S
Data
Data
t
o
SDA Bus
10 10
0
Signals from
the Slave
A
A
A
A
A
C
C
C
C
C
9
FN8123.0
March 29, 2005