CS7654 datasheet(26/62 Pages) CIRRUS

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CS7654

Address Set Operation

The ADDRESS SET format consists of a two-byte

packet which sets the address of a subsequent

READ operation. The first byte of the Station Ad-

dress with the LSB (data direction bit) set LOW to

indicate a write operation. The second byte is the

mat is the same as the WRITE format, without the

Read Operations in Three-Byte Mode

The READ operation may consist of two or more

bytes. The first byte is the station address with the

LSB (data direction bit) set HIGH indicating a read

operation. The addressed device then sends one or

more bytes back from the register last addressed by

the previous WRITE operation or the previous AD-

DRESS SET operation.

Operating CS7654 in Four-Byte I

2C Config-

uration

In this configuration the external controller talks

only to the CS7654 through the primary I2C inter-

face. All the other slave devices on the camera

board are tied to the secondary I2C port of the

CS7654. WRITE and READ packets only are de-

fined in four-byte mode. Independent address set

operations to slave devices on the secondary I2C

bus is not allowed in four-byte mode. Four-byte

mode is active when the P4BYTMODE pin (pin

46) is logic high.

Write Operations in Four-Byte mode

All WRITE operations from an external controller,

through the CS7654, to any slave device must use

the four-byte mode; this includes writing to the

CS7654 itself. The external controller sends a four-

byte WRITE command to the CS7654 which ini-

tiates a WRITE operation to the destination slave

device and sets the I2CBUSY bit in the status reg-

ister ( 01h at SA 0x34h ). The I2CBUSY bit is

cleared when the write operation on the secondary

bus is complete. The External controller can poll

the status register to check if the CS7654 has com-

pleted the command.

The CS7654 has a one-command-buffer which al-

lows the external controller to queue one additional

command while the current command is still being

executed. If more than one command is sent before

the I2CBUSY bit is cleared, the CS7654 saves only

the last command and executes it after the current

one is completed. Commands that involve writing

Byte Sequence

WRITE Format Packet Detail

First Byte

Station Address with LSB Set LOW

Second Byte

Device Register Address (0..255)

Third Byte

Table 6. WRITE Format Packet

Byte Sequence

ADDRESS SET format

Packet Details

First Byte

Station Address with LSB Set LOW

Second Byte

Device Register Address (0..255)

Table 7. ADDRESS SET Format Packet Operation

External

EPROM

CS7615

CS7654

controller

Figure 16. I

2C configuration showing primary

and secondary I

2C busses.

To other sub-systems

Byte Sequence

READ Format Packet Details

First Byte

Station Address with LSB set HIGH;

Source Device then Returns One

Byte of Register Data (0..255)

Second Byte

Returned data from CS7654

Table 8. READ Format Packet.

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