AR0130CS
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As a special case, in single frame mode, register writes
that occur after FV but before the next trigger will take effect
immediately on the next frame, as if there had been a Restart.
However, if the trigger for the next frame occurs during FV,
register writes take effect as with video mode.
Fields not identified as being frame−synchronized are
updated immediately after the register write is completed.
The effect of these registers on the next frame can be difficult
to predict if they affect the shutter pointer.
Restart
To restart the AR0130 at any time during the operation of
the sensor, write a “1” to the Restart register (R0x301A[1]
= 1). This has two effects: first, the current frame is
interrupted immediately. Second, any writes to
frame−synchronized registers and the shutter width registers
take effect immediately, and a new frame starts (in video
mode). The current row completes before the new frame is
started, so the time between issuing the Restart and the
beginning of the next frame can vary by about tROW.
Image Acquisition Modes
The AR0130 supports two image acquisition modes:
video (also known as master) and single frame.
Video
The video mode takes pictures by scanning the rows of the
sensor twice. On the first scan, each row is released from
reset, starting the exposure. On the second scan, the row is
sampled, processed, and returned to the reset state. The
exposure for any row is therefore the time between the first
and second scans. Each row is exposed for the same
duration, but at slightly different point in time, which can
cause a shear in moving subjects as is typical with electronic
rolling shutter sensors.
Single Frame
The single−frame mode operates similar to the video
mode. It also scans the rows of the sensor twice, first to reset
the rows and second to read the rows. Unlike video mode
where a continuous stream of images are output from the
image sensor, the single−frame mode outputs a single frame
in response to a high state placed on the TRIGGER input pin.
As long as the TRIGGER pin is held in a high state, new
images will be read out. After the TRIGGER pin is returned
to a low state, the image sensor will not output any new
images and will wait for the next high state on the TRIGGER
pin.
The TRIGGER pin state is detected during the vertical
blanking period (i.e. the FV signal is low). The pin is level
sensitive rather than edge sensitive. As such, image
integration will only begin when the sensor detects that the
TRIGGER pin has been held high for 3 consecutive clock
cycles.
During integration time of single−frame mode and video
mode, the FLASH output pin is at high.
Continuous Trigger
In certain applications, multiple sensors need to have their
video streams synchronized (E.g. surround view or
panorama view applications). The TRIGGER pin can also
be used to synchronize output of multiple image sensors
together and still get a video stream. This is called
continuous trigger mode. Continuous trigger is enabled by
holding the TRIGGER pin high. Alternatively, the
TRIGGER pin can be held high until the stream bit is
enabled (R0x301A[2]=1) then can be released for
continuous synchronized video streaming.
If the TRIGGER pins for all connected AR0130 sensors
are connected to the same control signal, all sensors will
receive the trigger pulse at the same time. If they are
configured to have the same frame timing, then the usage of
the TRIGGER pin guarantees that all sensors will be
synchronized within 1 PIXCLK cycle if PLL is disabled, or
2 PIXCLK cycles if PLL is enabled.
With continuous trigger mode, the application can now
make use of the video streaming mode while guaranteeing
that all sensor outputs are synchronized. As long as the initial
trigger for the sensors takes place at the same time, all
subsequent video streams will be synchronous.
Automatic Exposure Control
The integrated automatic exposure control (AEC) is
responsible for ensuring that optimal settings of exposure
and gain are computed and updated every other frame. AEC
can be enabled or disabled by R0x3100[0].
When AEC is disabled (R0x3100[0] = 0), the sensor uses
the manual exposure value in coarse and fine shutter width
registers and the manual gain value in the gain registers.
When AEC is enabled (R0x3100[0]=1), the target luma
value is set by R0x3102. For the AR0130 this target luma has
a default value of 0x0800 or about half scale.
The exposure control measures current scene luminosity
by accumulating a histogram of pixel values while reading
out a frame. It then compares the current luminosity to the
desired output luminosity. Finally, the appropriate
adjustments are made to the exposure time and gain. All
pixels are used, regardless of color or mono mode.
AEC does not work if digital binning is enabled.
Embedded Data and Statistics
The AR0130 has the capability to output image data and
statistics embedded within the frame timing. There are two
types of information embedded within the frame readout:
1. Embedded Data: If enabled, these are displayed on
the two rows immediately before the first active
pixel row is displayed.
2. Embedded Statistics: If enabled, these are
displayed on the two rows immediately after the
last active pixel row is displayed.
NOTE: Both embedded statistics and data must be
enabled and disabled together.