24C32A

DS21163E-page 6

 2004 Microchip Technology Inc.

4.0

WRITE OPERATION

4.1

Byte Write

Following the start condition from the master, the con-

trol code (four bits), the device select (three bits), 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 acknowl-

edge bit during the ninth clock cycle. Therefore, the

next byte transmitted by the master is the high-order

byte of the word address and will be written into the

address pointer of the 24C32A. The next byte is the

least significant address byte. After receiving another

acknowledge signal from the 24C32A the master

device will transmit the data word to be written into the

addressed memory location.

The 24C32A acknowledges again and the master gen-

erates a stop condition. This initiates the internal write

cycle, and during this time the 24C32A will not gener-

ate acknowledge signals (Figure 4-1).

4.2

Page Write

The write control byte, word address and the first data

byte are transmitted to the 24C32A in the same way as

in a byte write. But instead of generating a stop condi-

tion, the master transmits up to 32 bytes which are tem-

porarily 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 five lower

address pointer bits are internally incremented by one.

If the master should transmit more than 32 bytes 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).

Note:

Page write operations are limited to writing

bytes within a single physical page, regard-

less 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 neces-

sary for the application software to prevent

page write operations that would attempt to

cross a page boundary.

FIGURE 4-1:

BYTE WRITE

FIGURE 4-2:

PAGE WRITE

0000

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

S

T

A

R

T

CONTROL

BYTE

ADDRESS

HIGH BYTE

ADDRESS

LOW BYTE

DATA

A

C

K

A

C

K

A

C

K

A

C

K

S

T

O

P

S

P

000 0

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

S

T

A

R

T

CONTROL

BYTE

ADDRESS

HIGH BYTE

ADDRESS

LOW BYTE

DATA BYTE 0

A

C

K

A

C

K

A

C

K

A

C

K

S

T

O

P

DATA BYTE 31

S

P