34VL02 datasheet(7/32 Pages) MICROCHIP

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DS22079A-page 7

34VL02

FIGURE 3-1:

DATA TRANSFER SEQUENCE ON THE SERIAL BUS

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 34VL02 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 lev-

els on the corresponding A2, A1 and A0 pins for the

device to respond.

The eighth bit of slave address determines if the master

device wants to read or write to the 34VL02

(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 34VL02.

After receiving another Acknowledge signal from the

34VL02, the master device will transmit the data word to

be written into the addressed memory location. The

34VL02 acknowledges again and the master generates

a Stop condition. This initiates the internal write cycle,

which means that during this time, the 34VL02 will not

generate Acknowledge signals (Figure 4-1). If an

attempt is made to write to the array when the software

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 34VL02 in the same way as

in a byte write. Instead of generating a Stop condition,

the master transmits up to 15 additional data bytes to

the 34VL02, 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 gen-

erating the Stop condition, the address counter will roll

over and the previously received data will be overwrit-

ten. As with the byte write operation, once the Stop

condition is received, an internal write cycle will begin

SCL

SDA

(A)

(B)

(D)

(A)

(C)

Start

Condition

Address or

Acknowledge

Valid

Data

Allowed

to Change

Stop

Condition

Operation

Control

Code

Chip

Select

R/W

Read

1010

A2 A1 A0

Write

1010

A2 A1 A0

Write-Protect Register

0110

A2 A1 A0

Start

Read/Write

Slave Address

R/W A

011

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