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is turned off before the pattern is exposed. The post-exposure dark time refers to the
time that no pattern is displayed and the lighting is turned off after the pattern is
exposed. Thus, Pattern frame rate=1/(pre-exposure dark time + exposure time +
post-exposure dark time) can be obtained. It should be noted that although the final
effective frame rate can be calculated, the actual exposure time is less than 1/(frame
rate), which is caused by the existence of pre and post dark time.
6.7 Why is there a minimum pre-exposure dark time and
post-exposure dark time limit?
Pre-exposure dark time and post-exposure dark time are necessary for this
system. The system uses these unlit times to load the pattern onto the DMD, and the
user uses these unlit times to allow external cameras to properly capture and process
images.
6.8 What actually happens in pre-exposure dark time and
post-exposure dark time?
Inside the DLP controller a PWM sequence is used. A PWM sequence is a
specialized set of instructions used to tell LEDs when to turn on, when to turn off, and
for how long. This instruction set also helps control the loading of the pattern data
onto the DMD. Once the desired exposure time and pre-exposure dark time and
post-exposure dark time are set, the controller internally looks for a PWM sequence
that supports that timing. If the controller cannot find a PWM sequence that matches
this timing, then the DLPC347x controller will set the "Light Control Sequence Error
bit (bit 6)" in the "Short Status" register, which can be read by an I2C command
(0xD0).
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