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24LC41A Datasheet PDF : 18 Pages
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4.0 WRITE OPERATION
Write operations are identical for the DDC Monitor Port
(when in Bidirectional mode) and the Microcontroller
Access Port, with the exception of the VCLK and MWP
pins noted in the next sections. Data can be written
using either a Byte Write or Page Write command. Write
commands for the DDC Monitor Port and the
Microcontroller Access Port are completely
independent of one another.
4.1 Byte Write
Following the Start signal from the master, the slave
address (4-bits), the chip select bits (3-bits) and the
R/W bit which is a logic low is placed onto the bus by
the master transmitter. This indicates to the addressed
slave receiver that a byte with a word address will
follow after it has generated an Acknowledge bit during
the ninth clock cycle. Therefore, the next byte transmit-
ted by the master is the word address and will be
written into the address pointer of the port. After
receiving another Acknowledge signal from the port,
the master device will transmit the data word to be
written into the addressed memory location. The port
acknowledges again and the master generates a Stop
condition. This initiates the internal write cycle, and
during this time, the port will not generate Acknowledge
signals (see Figure 4-1).
For the DDC Monitor Port it is required that VCLK be
held at a logic high level in order to program the device.
This applies to byte write and page write operation.
Note that VCLK can go low while the device is in its
self-timed program operation and not affect program-
ming. The MWP pin must be held high for the duration
of the write protection.
24LC41A
4.2 Page Write
The write control byte, word address, and the first data
byte are transmitted to the port in the same way as in a
byte write. But, instead of generating a Stop condition,
the master transmits up to eight data bytes to the DDC
Monitor Port or 16 bytes to the Microcontroller Access
Port, which are temporarily stored in the on-chip page
buffer and will be written into the memory after the
master has transmitted a Stop condition. After the
receipt of each word, the three lower order address
pointer bits are internally incremented by one. The
higher order 5-bits of the word address remains
constant. If the master should transmit more than eight
words to the DDC Monitor Port or 16 words to the
Microcontroller Access Port prior to generating the Stop
condition, the address counter will roll over and the
previously received data will be overwritten. As with the
byte write operation, once the Stop condition is received
an internal write cycle will begin (see Figure 4-2).
For the DDC Monitor Port, it is required that VCLK be
held at a logic high level in order to program the device.
This applies to byte write and page write operation.
Note that VCLK can go low while the device is in its
self-timed program operation and not affect program-
ming. For the DDC Monitor Port, the MWP pin must be
held high for the duration of the write cycle.
Note:
Page write operations are limited to writing
bytes within a single physical page,
regardless of the number of bytes actually
being written. Physical page boundaries
Start at addresses that are integer
multiples of the page buffer size (or ‘page
size’) and end at addresses that are
integer multiples of [page size - 1]. If a
Page Write command attempts to write
across a physical page boundary, the
result is that the data wraps around to the
beginning of the current page (overwriting
data previously stored there), instead of
being written to the next page as might be
expected. It is therefore necessary for the
application software to prevent page write
operations that would attempt to cross a
page boundary.
2003 Microchip Technology Inc.
DS21176D-page 9
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