17
FN6370.3
August 18, 2008
Write Operations
Byte Write
For a write operation, the device requires the Slave Address
Byte and the Word Address Bytes. This gives the master
access to any one of the words in the array or CCR.
(Note: Prior to writing to the CCR, the master must write a
02h, then 06h to the status register in two preceding
operations to enable the write operation. See “Writing to the
Clock/Control Registers” on page 12. Upon receipt of each
address byte, the ISL12024 responds with an acknowledge.
After receiving both address bytes the ISL12024 awaits the
8 bits of data. After receiving the 8 data bits, the ISL12024
again responds with an acknowledge. The master then
terminates the transfer by generating a stop condition. The
ISL12024 then begins an internal write cycle of the data to
the non-volatile memory. During the 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 16).
A write to a protected block of memory is ignored, but will still
receive an acknowledge. At the end of the write command,
the ISL12024 will not initiate an internal write cycle, and will
continue to ACK commands.
Byte writes to all of the non-volatile registers are allowed,
except the DWAn registers which require multiple byte writes
or page writes to trigger non-volatile writes. See “Device
Operation” on page 12 for more information.
Page Write
The ISL12024 has a page write operation. It is initiated in the
same manner as the byte write operation; but instead of
terminating the write cycle after the first data byte is
transferred, the master can transmit up to 15 more bytes to
the memory array and up to 7 more bytes to the clock/control
registers. The RTC registers require a page write (8 bytes),
individual register writes are not allowed. (Note: Prior to
writing to the CCR, the master must write a 02h, then 06h to
the status register in two preceding operations to enable the
write operatio (see “Writing to the Clock/Control Registers”
on page 12.)
After the receipt of each byte, the ISL12024 responds with
an acknowledge, and the address is internally incremented
by one. The address pointer remains at the last address byte
written. When the counter reaches the end of the page, it
“rolls over” and goes back to the first address on the same
page. This means that the master can write 16 bytes to a
memory array page or 8 bytes to a CCR section starting at
any location on that page. For example, if the master begins
writing at location 10 of the memory and loads 15 bytes, then
the first 6 bytes are written to addresses 10 through 15, and
the last 6 bytes are written to columns 0 through 5.
Afterwards, the address counter would point to location 6 on
the page that was just written. If the master supplies more
than the maximum bytes in a page, then the previously
loaded data is over-written by the new data, one byte at a
time. (see Figure 17). The master terminates the Data Byte
loading by issuing a stop condition, which causes the
ISL12024 to begin the non-volatile write cycle. As with the
byte write operation, all inputs are disabled until completion
of the internal write cycle. See Figure 18 for the address,
acknowledge and data transfer sequence.
Stops and Write Modes
Stop conditions that terminate write operations must be sent
by the master after sending at least 1 full data byte and its
associated ACK signal. If a stop is issued in the middle of a
data byte, or before 1 full data byte + ACK is sent, then the
ISL12024 resets itself without performing the write. The
contents of the array are not affected.
S
T
A
R
T
S
T
O
P
SLAVE
ADDRESS
WORD
ADDRESS 1
DATA
A
C
K
A
C
K
A
C
K
SDA BUS
SIGNALS FROM
THE SLAVE
SIGNALS FROM
THE MASTER
0
A
C
K
WORD
ADDRESS 0
1111
0000000
FIGURE 16. BYTE WRITE SEQUENCE
ADDRESS
ADDRESS
10
6 BYTES
15
6 BYTES
ADDRESS = 5
ADDRESS POINTER ENDS
FIGURE 17. WRITING 12 BYTES TO A 16-BYTE MEMORY PAGE STARTING AT ADDRESS 10
AT ADDR = 5
ISL12024
