24AA00/24LC00/24C00

DS21178D-page 6

 2003 Microchip Technology Inc.

5.0

DEVICE ADDRESSING

After generating a Start condition, the bus master

transmits a control byte consisting of a slave address

and a Read/Write bit that indicates what type of

operation is to be performed. The slave address for the

24XX00 consists of a 4-bit device code ‘1010’ followed

by three don't care bits.

The last bit of the control byte determines the operation

to be performed. When set to a one a read operation is

selected, and when set to a zero a write operation is

selected. (Figure 5-1). The 24XX00 monitors the bus

for its corresponding slave address all the time. It

generates an Acknowledge bit if the slave address was

true and it is not in a Programming mode.

FIGURE 5-1:

CONTROL BYTE FORMAT

6.0

WRITE OPERATIONS

6.1

Byte Write

Following the Start signal from the master, the device

code (4 bits), the don't care 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 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 24XX00. Only the

lower four address bits are used by the device, and the

upper four bits are don’t cares. The 24XX00 will

acknowledge the address byte and the master device

will then transmit the data word to be written into the

addressed memory location. The 24XX00 acknowl-

edges again and the master generates a Stop

condition. This initiates the internal write cycle, and

during this time the 24XX00 will not generate Acknowl-

edge signals (Figure 7-2). After a byte Write command,

the internal address counter will not be incremented

and will point to the same address location that was just

written. If a Stop bit is transmitted to the device at any

point in the Write command sequence before the entire

sequence is complete, then the command will abort

and no data will be written. If more than 8 data bits are

transmitted before the Stop bit is sent, then the device

will clear the previously loaded byte and begin loading

the data buffer again. If more than one data byte is

transmitted to the device and a Stop bit is sent before a

full eight data bits have been transmitted, then the

Write command will abort and no data will be written.

is below 1.5V (24AA00 and 24LC00) or 3.8V (24C00)

at nominal conditions.

10

1

0

X

X

X

SACK

R/W

Device Select

Bits

Don’t Care

Bits

Slave Address

Acknowledge Bit

Start Bit

Read/Write Bit