24VL014HSLASHP datasheet(8/28 Pages) MICROCHIP

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24VL014H

DS22116A-page 8

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 24VL014H 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 24VL014H 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.

The last bit of the control byte defines the operation to

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

selected. When set to a ‘0’, a write operation is

selected. Following the Start condition, the 24VL014H

monitors the SDA bus, checking the control byte being

transmitted. Upon receiving a ‘1010’ code and

appropriate

Chip

Select

bits,

the

slave

device

outputs an Acknowledge signal on the SDA line.

Depending on the state of the R/W bit, the 24VL014H

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 and A0 can be used to

expand the contiguous address space for up to 8K bits

by adding up to eight 24VL014H devices on the same

bus. In this case, software can use A0 of the control

byte as address bit A7, A1 as address bit A8, and A2

as address bit A9. It is not possible to sequentially read

across device boundaries.

SACK

R/W

Control Code

Chip Select

Bits

Slave Address

Acknowledge Bit

Start Bit

Read/Write Bit

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