24LC41

DS21140F-page 8

 2004 Microchip Technology Inc.

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/DWP 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 (Figure 4-1).

For the DDC Monitor Port it is required that VCLK/DWP

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/DWP can go low while the

device is in its self-timed program operation and not

affect programming.

For the Microcontroller Access Port, the MWP pin must

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 (Figure 4-2).

For the DDC Monitor Port, it is required thatVCLK/

DWP 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/DWP can go low while the

device is in its self-timed program operation and not

affect programming.

For the Microcontroller Access Port, the MWP pin must

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 multi-

ples 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.