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 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.
The user controls and configures HDJD-J822 by pro-
gramming a set of internal registers. The registers are
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.
2
programmed through the I C 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:
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.
• Positive sensor slope
• Internal reference voltage
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.
• 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.
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).
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.
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
:
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).
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
2
registers via I C 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.
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.
6
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