MCP79411 datasheet(39/60 Pages) MICROCHIP

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DS20002266E-page 39

MCP79410/MCP79411/MCP79412

10.2.3

EEPROM BYTE WRITE

Following the Start condition from the master, the

control code and the R/W bit (which is a logic low) are

clocked 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 transmitted by the master is

the word address and will be written into the Address

Pointer of the MCP7941X. After receiving another

Acknowledge signal from the MCP7941X, the master

device transmits the data word to be written into the

addressed

memory

location.

The

MCP7941X

acknowledges again and the master generates a Stop

condition. This initiates the internal write cycle, and,

during this time, the MCP7941X does not generate

Acknowledge signals for EEPROM Write commands.

Access to the RTCC/SRAM registers is possible during

an EEPROM write cycle.

If an attempt is made to write to an address and the

protection is set then the device will acknowledge the

command but no write cycle will occur, no data will be

written, and the device will immediately accept a new

command. After a byte Write command, the internal

address counter will point to the address location

following the one that was just written.

10.2.4

EEPROM PAGE WRITE

The write control byte, word address, and the first data

byte are transmitted to the MCP7941X in the same way

as in a byte write. But instead of generating a Stop

condition, the master transmits up to seven additional

bytes (MCP7941X has an 8-byte page), which are

temporarily stored in the on-chip page buffer and will be

written into memory after the master has transmitted a

Stop condition. After receipt of each word, the three

lower Address Pointer bits are internally incremented

by one. If the master should transmit more than eight

bytes prior to generating the Stop condition, the

address counter will roll over and the data received

previously will be overwritten. As with the byte write

operation, once the Stop condition is received, an

internal write cycle will begin (Figure 10-4).

Note:

Page write operations are limited to writing

bytes within a single physical page,

regardless of the number of bytes actually

being

transmitted.

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.

Note:

Addressing undefined EEPROM locations

will

result

the

MCP7941X

not

acknowledging the address.

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