ST STM32L4+ Series Reference Manual page 773

RM0432
DCMI_HSYNC
DCMI_VSYNC
1. Here, the active state of DCMI_HSYNC and DCMI_VSYNC is 1.
2. DCMI_HSYNC and DCMI_VSYNC can change states at the same time.
In continuous grab mode, the FCRC[1:0] bits in DCMI_CR can be configured to grab all
pictures, every second picture or one out of four pictures to decrease the frame capture
rate.
Note: In the hardware synchronization mode (ESS = 0 in DCMI_CR), the IT_VSYNC interrupt is
generated (if enabled) even when CAPTURE = 0 in DCMI_CR so, to reduce the frame
capture rate even further, the IT_VSYNC interrupt can be used to count the number of
frames between 2 captures in conjunction with the Snapshot mode. This is not allowed by
embedded data synchronization mode.
24.3.8 DCMI crop feature
With the crop feature, the camera interface can select a rectangular window from the
received image. The start (upper left corner) coordinates and size (horizontal dimension in
number of pixel clocks and vertical dimension in number of lines) are specified using two
32-bit registers (DCMI_CWSTRT and DCMI_CWSIZE). The size of the window is specified
in number of pixel clocks (horizontal dimension) and in number of lines (vertical dimension).
These registers specify the coordinates of the starting point of the capture window as a line
number (in the frame, starting from 0) and a number of pixel clocks (on the line, starting from
0), and the size of the window as a line number and a number of pixel clocks. The CAPCNT
value can only be a multiple of 4 (two least significant bits are forced to 0) to allow the
correct transfer of data through the DMA.
Figure 172. Frame capture waveforms in continuous grab mode
Figure 173. Coordinates and size of the window after cropping
HOFFCNT[13:0]
in
DCMI_CWSTRT
RM0432 Rev 6
Frame 1 captured
VST[12:0] in DCMI_CWSTRT
VLINE[13:0] in DCMI_CWSIZE
CAPCNT[13:0] in DCMI_CWSIZE
Digital camera interface (DCMI)
Frame 2 captured
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