24LC128-ISLASHST datasheet(16/42 Pages) MICROCHIP

16 / 42 page

24AAXX/24LCXX/24FCXX

DS21930B-page 16

6.0

WRITE OPERATIONS

6.1

Byte Write

A byte write operation begins with a Start condition

from the master followed by the four-bit control code

(see Figure 6-1 and Figure 6-2). The next 3 bits are

either the Block Address bits (for devices without

address pins) or the Chip Select bits (for devices with

address pins). Then the master transmitter clocks the

R/W bit (which is a logic low) onto the bus. The slave

then generates an Acknowledge bit during the ninth

clock cycle.

The next byte transmitted by the master is the address

byte (for 128-bit to 16 Kbit devices) or the high-order

address byte (for 32-512 Kbit devices). For 32 through

512 Kbit devices, the high-order address byte is

followed by the low-order address byte. In either case,

each address byte is acknowledged by the 24XX and

the address bits are latched into the internal address

counter of the 24XX.

For the 24XX00 devices, only the lower four address

bits are used by the device. The upper four bits are

“don’t cares.”

After receiving the ACK from the 24XX acknowledging

the final address byte, the master device transmits the

data word to be written into the addressed memory

location. The 24XX acknowledges again and the

master generates a Stop condition, which initiates the

internal write cycle.

If an attempt is made to write to an array with the WP

pin held high, 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 increment to the next address

location. During a write cycle, the 24XX will not

acknowledge commands.

FIGURE 6-1:

BYTE WRITE: 128-BIT TO 16 KBIT DEVICES

FIGURE 6-2:

BYTE WRITE: 32 TO 512 KBIT DEVICES

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Address

Byte

Data

Byte

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

High Order

Address Byte

Low Order

Address Byte

Data

Byte

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