ASX340 datasheet(41/78 Pages) ETC2

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ASX340/MT9V139_DS Rev. C Pub. 3/11 EN

ASX340/MT9V139: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor

Slave Two-Wire Serial Interface

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Preliminary

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 ASX340/MT9V139 are 0x90 (write address) and 0x91 (read

address). Alternate slave addresses of 0xBA (write address) and 0xBB (read address) can

be selected by asserting the SADDR input signal.

Message Byte

Message bytes are used for sending register addresses and register write data to the slave

device and for retrieving register read data. The protocol used is outside the scope of the

two-wire serial interface specification.

Acknowledge Bit

Each 8-bit data transfer is followed by an acknowledge bit or a no-acknowledge bit in the

SCLK clock period following the data transfer. The transmitter (which is the master when

writing, or the slave when reading) releases SDATA. The receiver indicates an acknowl-

edge bit by driving SDATA LOW. As for data transfers, SDATA can change when SCLK is

LOW and must be stable while SCLK is HIGH.

No-Acknowledge Bit

The no-acknowledge bit is generated when the receiver does not drive SDATA low during

the SCLK clock period following a data transfer. A no-acknowledge bit is used to termi-

nate a read sequence.

Stop Condition

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

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