Camera module Trigger Mode manual
This AN mainly introduces the trigger mode of global shutter camera module, including hardware trigger and software trigger.
1 Applicable Product models
2 The concept of image synchronization mode
2.1 Free Running
In this mode, the camera module runs on its own.
2.2 Hardware Trigger
In this mode,The Trigger IO pin is used as the trigger signal, and the module begins to expose and output the image after receiving the trigger signal.
Pin definition：CS-MIPI-SC132 DataSheet
Triggger edge, trigger delay and trigger debouncer attribute supported.
triggeredge：trigger edge
tgdly：trigger delay
tgdebncr：debouncer
2.3 Software Trigger
In this mode，Use the I2C register to trigger an image.
striggerone： trigger an image
Note：The above instructions refer to CS Serial I2C setting .
3 Exposure control and maximum frame rate in Trigger mode
3.1 Configuration of exposure and gain in Trigger mode
In trigger mode, it is recommended that users use manual exposure. Of course, the automatic exposure mode can also be used,
but because the AE algorithm needs to go through some frames to converge, the exposure effect of the first few frames will not be good.
expmode：exposure mode setting
metime：manual exposure time
meagain：manual analog gain
medgain：manual digital gain
You can use the expostate instruction to read out the current exposure time and gain value in automatic mode as a reference.
Note：The above instructions refer to CS Serial I2C setting .
3.2 Exposure time and Transmission time in Trigger mode
Ttgmin = Texp + Ttrans
Ttgmin：minimum trigger interval
Texp：exposure time
Ttrans：transmission time of one frame
Accordingly, if the minimum trigger interval is known, the maximum allowable exposure time is:
Texpmax = Ttgmin - Ttrans
Texpmax：maximum exposure time
If the time interval between the current trigger signal and the previous trigger signal is smaller than the minimum interval time,
the sensor will ignore the current trigger signal.
- Texp：exposure time
Users can set it to automatical or manual.
expmode is auto : set max exposure time via aetime.
expmode is manual : set exposure time via metime.
- Ttrans：transmission time of one frame
The transmission time of a frame is related to the current resolution mode.
| Video Format | Ttrans（ms） | Max Framerate | Maximum exposure time to guarantee maximum framerate（ms） |
|---|---|---|---|
| 1280x1080
1080x1280 |
18.67 | 45 | 3.55 |
| 1280x720
720x1280 |
14.94 | 60 | 1.73 |
| 640x480
480x640 |
7.65 | 120 | 0.68 |
4 Delay in trigger mode
Ttotal = tgdly + Texp + Ttrans +Tisp+Tmipi
Ttotal ：the total trigger delay is the time from the trigger signal to the complete image output through the MIPI signal.
tgdly：trigger delay time, the following measurements are configured to 0. tgdly is valid only for Hardware trigger mode.
Texp exposure time，the following is based on the actual values read by expostate.
Tisp：image signal processing time.
Tmipi：MIPI transmission time.
| Video Format | Texp（us） | Ttotal（ms） |
|---|---|---|
| 1280x1080 | 1000 | 45.80 |
| 1080x1280 | 1000 | 43.20 |
| 1280x720 | 1000 | 35.20 |
| 720x1280 | 1000 | 33.40 |
| 640x480 | 1000 | 18.00 |
| 480x640 | 1000 | 17.20 |