HDJD-J822-SCR00 datasheet(6/16 Pages) AVAGO

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High Level Description

A hardware reset (by asserting XRST) should be per-

formed before starting any operation. It is assumed that

factory calibration was performed prior to deployment

of HDJD-J822. Calibration is discussed at the end of this

section.

The user controls and configures HDJD-J822 by pro-

gramming a set of internal registers. The registers are

programmed through the I2C protocol – a standard, syn-

chronous, serial interface. The registers define operation

modes such as sensor slope, reference voltage selection,

color space format, PWM assertion level, etc. Selection

between internal and external clock can only be made

through pin setup.

A typical set-up would be:

• Positive sensor slope

• Internal reference voltage

• 100 Hz (nominal) sensor

sample rate

• 610 Hz PWM (nominal)

• Active-high PWM output

• 2.5 MHz (nominal) internal

oscillator

HDJD-J822 resets into an “idle” mode and the PWM out-

puts are held low.

If the PWM assertion level bit (PWML) of register CONFIG1

is changed to high, the PWM outputs will then be held

high. However, since the reset condition for that register

bit is low, HDJD-J822 always resets with the PWM outputs

held low.

The next step after setting up the device is to write the

calibration data to the calibration registers (address 0x8A

to 0xA8). The calibration data is typically stored in an exter-

nal non-volatile memory. After writing the data, the user

can set the PWM enable bit (PWME) of register CTRL1 to

begin normal operation.

The operation begins with the processor taking in the tri-

color sensor’s digitized readings from the internal ADC.

That data is compared to the desired color/brightness

setting. The PWM duty factor is adjusted in response to

any error signal generated by that comparison operation.

The user can change the color/brightness setting at any

time by writing to the appropriate device registers (ad-

dress 0xE8 to 0xED during normal operation).

The feedback and processing operation is repeated at a

rate of 100 Hz (nominal).

The PWM signal is applied to the LED drivers and controls

the on-time duration of the red, green and blue LEDs.

The user can input the desired color/brightness in a va-

riety of color formats such as CIE XYZ, Yxy, Yu’v’ and RGB

(illuminant E).

There are three indicators in register ERROR that monitor

the status of the color management system. Refer to Ap-

plication Note 5070.

Factory calibration is needed at a system level to create a

‘snapshot’of the initial conditions of the system. The color

management algorithm references the snapshot data. In

effect, the calibration data trims out variation in the en-

tire signal chain from LEDs to sensor to filter to ADC. The

calibration discussion below is brief. Refer to Application

Note 5070 for detailed calibration procedures.

First, the device is put into “open loop” mode by setting

the OPMD bit of register CONFIG1 to high. In open loop

mode, the color management algorithm is turned off.

Second, all LEDs are switched on to maximum PWM. Dur-

ing this, the ADC output is read out to check if the sensor

output is within the dynamic range of the system i.e., 400

< pass < 800. An optional internal 2x gain (1) can be se-

lected if the ADC reading is less than 400. This procedure

is performed for each sensor channel.

Next, only the RED LEDs are switched on. An external

camera must be set up to capture the CIE co-ordinates

(preferably XYZ) of the RED LEDs. The scaled XYZ readings

are then sent to the RED LED camera calibration registers

(address 0xE8 to 0xED during calibration mode). Next,

the GSSR bit of register CTRL2 is set to capture the sensor

readings of the RED LEDs. The readings are stored in the

ADC reading registers (SENSOR_ADCZ, SENSOR_ADCY,

SENSOR_ADCX registers). The user must read those reg-

isters and transfer them to the RED LED sensor calibration

registers (address 0xFA to 0xFF).

This is repeated for GREEN and BLUE LEDs.

The RCAL bit of register CTRL2 is then set, after which

HDJD-J822 will compute the 31 bytes of calibration data

CAL_DATA0 to CAL_DATA30 (2)

The 2 pieces of calibration data is noted as (1), and (2)

above. The user will need to read them from the device

registers via I2C and store them in an external non-vola-

tile memory. They will have to be written to the appropri-

ate registers prior to the start of normal operation, and

should be part of the system boot-up sequence.

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