M34A02

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For correct device operation, Serial Data (SDA)

must be stable before the rising edge of Serial

Clock (SCL), and the data must change

Serial Clock (SCL) is Low.

Memory Addressing

To start communication between the bus master

and the slave device, the bus master must initiate

a Start condition. Following this, the bus master

sends the 8-bit byte, shown in Table 3, on Serial

Data (SDA) (most significant bit first). This

consists of the 7-bit Device Select code, and the

Read/Write bit (RW).

The Device Select Code consists of a 4-bit Device

Type Identifier, and a 3-bit Chip Enable “Address”

(E2, E1, E0). To address the memory array, the 4-

bit Device Type Identifier is 1011b.

Up to eight memory devices can be connected on

a single bus. Each one is given a unique 3-bit code

on Chip Enable (E0, E1, E2). When the Device

Select Code is received on Serial Data (SDA), the

device only responds if the Chip Select Code is the

Figure 5. ACR Serial Bus Protocol

SCL

SDA

SCL

SDA

SDA

START

Condition

SDA

Input

SDA

Change

AI00792B

STOP

Condition

1

23

7

89

MSB

ACK

START

Condition

SCL

1

23

7

89

MSB

ACK

STOP

Condition

Note: 1. The most significant bit, b7, is sent first.

Device Type Identifier

Chip Enable

RW

b7

b6

b5

b4

b3

b2

b1

b0

Device Select Code

1

0

1

1

E2

E1

E0

RW