A1454

8

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

The master controls the A1454 by programming it as a slave.

To do so, the master transmits data bits to the SDA input of the

A1454, in synchronization with the clocking signal the master

transmits simultaneously on the SCL input.

A complete transmission begins with the master pulling SDA low

(Start bit), and completes with the master releasing the SDA line

(Stop bit). As shown in figure 1, between these points, the master

transmits two address bytes, the first with the A1454 (chip)

address bits and a write command bit (D0 = 0) and the second

with the initial target register address, which are followed by the

data bytes. After every byte, regardless of byte payload, the slave

A1454 acknowledges by transmitting a low to the master on the

SDA line.

in Figure 2. After the slave acknowledges a data byte, instead of

sending a Stop bit, the master sends the next data byte. Only after

the final data byte is written and the slave acknowledges, does the

master provide a Stop bit. The A1454 automatically directs each

additional data byte to the next register, in order of regiter address

number. Note that only the initial register address is required.

This allows faster data entry, although it restricts data entry to

sequential registers. If non-sequential registers are to be written,

separate write commands can be sent.

A1454 (Slave) Acknowledge

A1454 (Slave) Acknowledge

A1454 (Slave) Acknowledge

A1454 (Slave) Acknowledge

A1454 (Slave) Acknowledge

A1454 (Slave) Acknowledge

Write bit

Write bit

Slave Address

Slave Data1

Start

Register Address

Register Data2

Register Data0

Register Data3

SDA

SDA

SCL

SCL

D6

D6

D5

D5

D4

D4

D3

D3

D2

D2

D1

D1

D0

D0

W AK

AK

D7

D7

D7

D6

D6

D5

D5

D4

D4

D3

D3

D2

D2

D1

D1

D0

D0

AK

AK

D7

D7

D6

D6

D5

D5

D4

D4

D3

D3

D2

D2

D1

D1

D0

D0

AK

AK

Stop

. . .

. . .

. . .

. . .

1

1

1

1

1

1

2

2

2

2

2

2

3

3

3

3

3

3

4

4

4

4

4

4

5

5

5

5

5

5

6

6

6

6

6

6

7

7

7

7

7

7

8

8

8

8

8

8

9

9

9

9

9

9

Customer Write Access

Before attempting to write to any of the serial registers or

EEPROM memory locations in the A1454, an access code must

be entered, to put the device in customer access mode. If cus-

tomer access mode is configured, then no writes to the device

are allowed. The only exception this this is the SLEEP bit, which

can be written regardless of the access mode. Furthermore, any

register or EEPROM location can be read at any time regardless

of the access mode.

To enter either customer access mode, an access command needs

write operation with the address and data values as shown in

Table 2. Once the access mode is set, it is not possible to change

the mode without power-cycling the device. There is no time

limit for entering the code.

Table 5: Customer Access Code

Address

Data

Customer Access Mode

0x24

0x2C413534