24C01CSN datasheet(8/36 Pages) MICROCHIP

8 / 36 page

24C01C

DS21201K-page 8

 1997-2012 Microchip Technology Inc.

5.0

DEVICE ADDRESSING

A control byte is the first byte received following the

Start condition from the master device (Figure 5-1).

The control byte consists of a four-bit control code; for

the 24C01C this is set as ‘1010’ binary for read and

write operations. The next three bits of the control byte

are the Chip Select bits (A2, A1, A0). The Chip Select

bits allow the use of up to eight 24C01C devices on the

same bus and are used to select 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. These bits

are in effect the three Most Significant bits of the word

address.

For the SOT-23 package, the A2 address pin is not

available. During device addressing, the A2 Chip

Select bit should be set to ‘0’.

The last bit of the control byte defines the operation to

be performed. When set to a ‘1’ a read operation is

selected, and when set to a ‘0’ a write operation is

selected. Following the Start condition, the 24C01C

monitors the SDA bus checking the control byte being

transmitted. Upon receiving a ‘1010’ code and appro-

priate Chip Select bits, the slave device outputs an

Acknowledge signal on the SDA line. Depending on the

state of the R/W bit, the 24C01C will select a read or

write operation.

FIGURE 5-1:

CONTROL BYTE

FORMAT

5.1

Contiguous Addressing Across

Multiple Devices

The Chip Select bits A2, A1, A0 can be used to expand

the contiguous address space for up to 8K bits by

adding up to eight 24C01C devices on the same bus.

In this case, software can use A0 of the control byte as

address bit A8, A1 as address bit A9, and A2 as

address bit A10. It is not possible to sequentially read

across device boundaries.

For the SOT-23 package, up to four 24C01C devices

can be added for up to 4K bits of address space. In this

case, software can use A0 of the control byte as

address bit A8, and A1 as address bit A9. It is not pos-

sible to sequentially read across device boundaries.

A2 A1 A0

SACK

R/W

Control Code

Chip Select

Bits

Slave Address

Acknowledge Bit

Start Bit

Read/Write Bit

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