ISL12025 Datasheet, PDF (18/27 Pages) Intersil Corporation – Real-Time Clock/Calendar with I2C Bus and EEPROM

ISL12025
operation is selected. A zero selects a write operation. (see
Figure 19).
After loading the entire Slave Address Byte from the SDA
bus, the ISL12025 compares the device identifier and device
select bits with ‘1010111’ or ‘1101111’. Upon a correct
compare, the device outputs an acknowledge on the SDA
line.
Following the Slave Byte is a two byte word address. The
word address is either supplied by the master device or
obtained from an internal counter. On power-up, the internal
address counter is set to address 0h, so a current address
read of the EEPROM array starts at address 0. When
required, as part of a random read, the master must supply
the 2 Word Address Bytes as shown in Figure 19.
In a random read operation, the slave byte in the “dummy
write” portion must match the slave byte in the “read”
section. That is if the random read is from the array the slave
byte must be 1010111x in both instances. Similarly, for a
random read of the Clock/Control Registers, the slave byte
must be 1101111x in both places.
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 13.) Upon receipt of each
address byte, the ISL12025 responds with an acknowledge.
After receiving both address bytes the ISL12025 awaits the
eight bits of data. After receiving the 8 data bits, the
ISL12025 again responds with an acknowledge. The master
then terminates the transfer by generating a stop condition.
The ISL12025 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 20).
A write to a protected block of memory is ignored, but will still
receive an acknowledge. At the end of the write command,
the ISL12025 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 nonvolatile writes. See “Device
Operation” on page 13 for more information.
Page Write
The ISL12025 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 operation. See “Writing to the Clock/Control Registers”
on page 13.)
After the receipt of each byte, the ISL12025 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 21). The master terminates the Data Byte
loading by issuing a stop condition, which causes the
ISL12025 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 22 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
ISL12025 resets itself without performing the write. The
contents of the array are not affected.
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FN6371.3
August 13, 2008