AR0134CSSC00SUEAH-GEVB datasheet(17/41 Pages) ONSEMI

17 / 41 page

AR0134_DS Rev. G Pub. 6/15 EN

©Semiconductor Components Industries, LLC,2015.

AR0134: 1/3-Inch 1.2 Mp CMOS Digital Image Sensor

Two-Wire Serial Register Interface

The two-wire serial interface bus enables read/write access to control and status regis-

ters within the AR0134.The interface protocol uses a master/slave model in which a

master controls one or more slave devices. The sensor acts as a slave device. The master

generates a clock (SCLK) that is an input to the sensor and is used to synchronize trans-

fers. Data is transferred between the master and the slave on a bidirectional signal

(SDATA). SDATA is pulled up to VDD_IO off-chip by a 1.5k resistor. Either the slave or

master device can drive SDATA LOW—the interface protocol determines which device is

allowed to drive SDATA at any given time.

The protocols described in the two-wire serial interface specification allow the slave

device to drive SCLK LOW; the AR0134 uses SCLK as an input only and therefore never

drives it LOW.

Protocol

Data transfers on the two-wire serial interface bus are performed by a sequence of low-

level protocol elements:

1. a (repeated) start condition

2. a slave address/data direction byte

3. an (a no) acknowledge bit

4. a message byte

5. a stop condition

The bus is idle when both SCLK and SDATA are HIGH. Control of the bus is initiated with a

start condition, and the bus is released with a stop condition. Only the master can

generate the start and stop conditions.

Start Condition

A start condition is defined as a HIGH-to-LOW transition on SDATA while ScLK is HIGH.

At the end of a transfer, the master can generate a start condition without previously

generating a stop condition; this is known as a “repeated start” or “restart” condition.

Stop Condition

A stop condition is defined as a LOW-to-HIGH transition on SDATA while ScLK is HIGH.

Data Transfer

Data is transferred serially, 8 bits at a time, with the MSB transmitted first. Each byte of

data is followed by an acknowledge bit or a no-acknowledge bit. This data transfer

mechanism is used for the slave address/data direction byte and for message bytes.

One data bit is transferred during each SCLK clock period. SDATA can change when ScLK is

LOW and must be stable while ScLK is HIGH.

Slave Address/Data Direction Byte

Bits [7:1] of this byte represent the device slave address and bit [0] indicates the data

transfer direction. A “0” in bit [0] indicates a WRITE, and a “1” indicates a READ. The

default slave addresses used by the AR0134 are 0x20 (write address) and 0x21 (read

address) in accordance with the specification. Alternate slave addresses of 0x30 (write

address) and 0x31 (read address) can be selected by enabling and asserting the SADDR

input.

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