24LCS52-SLASHMCG datasheet(6/28 Pages) MICROCHIP

6 / 28 page

24AA52/24LCS52

DS21166J-page 6

3.6

Device Addressing

A control byte is the first byte received following the

Start condition from the master device. The first part of

the control byte consists of a 4-bit control code which is

set to ‘1010’ for normal read and write operations and

‘0110’ for writing to the write-protect register. The

control byte is followed by three Chip Select bits (A2,

A1, A0). The Chip Select bits allow the use of up to

eight 24XXX52 devices on the same bus and are used

to determine which device is accessed. The Chip

Select bits in the control byte must correspond to the

logic levels on the corresponding A2, A1 and A0 pins

for the device to respond. The device will not acknowl-

edge if you attempt a Read command with the control

code set to ‘0110’.

The eighth bit of slave address determines if the master

device wants to read or write to the 24XXX52

(Figure 3-2). When set to a one, a read operation is

selected. When set to a zero, a write operation is

selected.

FIGURE 3-2:

CONTROL BYTE

ALLOCATION

4.0

WRITE OPERATIONS

4.1

Byte Write

Following the Start signal from the master, the device

code(4 bits), the Chip Select bits (3 bits) and the R/W

bit, which is a logic low, are placed onto the bus by the

master transmitter. This indicates to the addressed

slave receiver that a byte with a word address will follow,

once 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 24XXX52.

After receiving another Acknowledge signal from the

24XXX52, the master device will transmit the data word

to be written into the addressed memory location. The

24XXX52 acknowledges again and the master gener-

ates a Stop condition. This initiates the internal write

cycle, which means that during this time, the 24XXX52

will not generate Acknowledge signals (Figure 4-1). If

an attempt is made to write to the array when the soft-

ware or hardware write protection has been enabled,

the device will acknowledge the command, but no data

will be written. The write cycle time must be observed

even if the write protection is enabled.

4.2

Page Write

The write control byte, word address and the first data

byte are transmitted to the 24XXX52 in the same way

as in a byte write. Instead of generating a Stop condi-

tion, the master transmits up to 15 additional data bytes

to the 24XXX52, 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. Upon

receipt of each word, the four lower order Address

Pointer bits are internally incremented by one. The

higher order four bits of the word address remain

constant. If the master should transmit more than 16

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). If an attempt

is made to write to the array when the hardware write

protection has been enabled, the device will acknowl-

edge the command, but no data will be written. The

write cycle time must be observed even if the write

protection is enabled.

Operation

Control

Code

Chip

Select

R/W

Read

1010

A2 A1 A0

Write

1010

A2 A1 A0

Set Write-Protect

0110

A2 A1 A0

Start

Read/Write

Slave Address

R/W A

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 mul-

tiples of [page size – 1]. If a Page Write

command attempts to write across a phys-

ical 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.

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