CS7654 datasheet(25/62 Pages) CIRRUS

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CS7654

INTERNAL REGISTER STRUCTURE

AND USER INTERFACE

The user interface describes the user’s external

view of the CS7654 and the basic control opera-

tions. These areas include digital data, analog out-

put

modes

and

organization,

timing

and

synchronization signals, I2C interface, and miscel-

laneous controls.

The CS7654 has two I2C ports: (1) a slave I2C port

called the primary I2C port, and (2) a secondary I2C

port with limited I2C master capabilities. The pri-

mary I2C port allows an external controller to con-

trol the CS7654 ( See Station Address section for

more details on Station Address structure ). It is as-

sumed the external controller will also directly con-

trol any other I2C slave devices on the camera

board. This is the normal I2C operation mode of

CS7654. The secondary I2C port, on the other

hand, may be used to control all the other slave de-

vices on a camera board through the CS7654 only.

This feature is useful when the external I2C con-

troller is used to control multiple cameras. When

used in this configuration the P4BYTMODE pin

(pin 46) of the CS7654 must be tied high and the

device is operated in four-byte mode.

Operating CS7654 in Normal I2C

Configuration (Three-Byte Mode)

In normal mode, the CS7654 is connected as a

slave device to an external I2C controller through

the primary I2C port. The connection is done via a

two-wire serial bus. Other I2C devices on the cam-

era may also share the same serial bus. The external

controller communicates with the I2C devices by

sending and receiving short packets of 8-bit words

in accordance with the I2C protocol. The packets

contain the station address of the target device, the

desired register address, and data.

There are three packet formats: WRITE format,

ADDRESS SET format, and READ format. Each

packet is addressed to a device by the station ad-

dress. The LSB of the station address is the R/W

(data direction) bit. This bit is set LOW in the

WRITE and ADDRESS SET packets, and it is set

HIGH for READ packets. The master can read and

write to non-existent registers within the selected

device. WRITE operations will have no effect;

READ operations will return a value of 00h.

Station Address

Each device on the I2C bus has a unique 7-bit ad-

dress. An eighth bit, the R/W bit, determines if the

current data transfer writes data to the slave device

or reads data from the slave device. It is common to

represent the station address and R/W bit as two 8-

bit station addresses, one address for write accesses

and another address for read accesses. We will fol-

low this practice. Please note that because the reg-

ister of the CS7654 are physically implemented in

two different banks, the use of two different Station

Addresses are necessary. Therefore, to access the

proper registers you must first select the proper Sta-

tion Address. Both Station Adresses have to be dif-

ferent from one another or an internal register

conflict will occur.

The CS7654 default station address are 34h for

writes and 35h for reads for the color processing

section and 00h and 01h for the encoder portion of

the CS7654. The station address can be changed by

writing a new station address to register FFh. The

value written to this register does not include the

R/W bit. For example. The default station address

(34h write / 35h read) will be stored as 1Ah in reg-

ister FFh.

Write Operations in Three-Byte Mode

The WRITE format consists of a three-byte packet.

The first byte is the station address with the data di-

rection bit set LOW to indicate a write. The second

byte is the device register address (0..255). The

third byte is the register data (0..255). No addition-

al bytes are allowed.

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