ASX340AT datasheet(33/75 Pages) ONSEMI

33 / 75 page

ASX340AT/D Rev. H, 8/15 EN

©Semiconductor Components Industries, LLC, 2015.

ASX340CS: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor

External Signal Processing

Command Flow

The host issues a command by writing (through a two-wire interface bus) to the

command register. All commands are encoded with bit 15 set, which automatically

generates the host command (doorbell) interrupt to the microprocessor.

Assuming initial conditions, the host first writes the command parameters (if any) to the

parameters pool (in the command handler's logical page), then writes the command to

command register. The firmware interrupt handler then signals the Command Handler

task to process the command.

If the host wishes to determine the outcome of the command, it must poll the command

completed processing the command. When the doorbell bit is cleared, the contents of

the command register indicate the command's result status. If the command generated

response parameters, the host can now retrieve these from the parameters pool.

Note:

The host must not write to the parameters pool, nor issue another command, until

the previous command completes. This is true even if the host does not care about the

result of the previous command. Therefore, the host must always poll the command

issuing a command.

For a complete command list and further information consult the Host Command Inter-

face Specification.

An example of how (using DevWare) a command may be initiated in the form of a

“Preset” follows.

Issue the SYSMGR_SET_STATE Command

All DevWare presets supplied by ON Semiconductor poll and test the doorbell bit after

issuing the command. Therefore there is no need to check if the doorbell bit is clear

before issuing the next command.

# Set the desired next state in the parameters pool(SYS_STATE_ENTER_CON-

FIG_CHANGE)

REG= 0xFC00, 0x2800 // CMD_HANDLER_PARAMS_POOL_0

# Issue the HC_SYSMGR_SET_STATE command

REG= 0x0040, 0x8100 // COMMAND_REGISTER

# Wait for the FW to complete the command (clear the Doorbell bit)

POLL_FIELD= COMMAND_REGISTER, DOORBELL,!=0, DELAY=10, TIMEOUT=100

# Check the command was successful

ERROR_IF= COMMAND_REGISTER, HOST_COMMAND,!=0, "Set State command

failed",

ASX340AT Datasheet(PDF) 33 Page - ON Semiconductor