Hi,
This bit should limit the minimum output level from the encoder. To evaluate you would need to send luma values below the blanking level to the encoder. Additionally you would also need to do the following writes:
1. 0x82[7] = 0 - Disables active video edge contol and allows the luma level to go below the blanking level.
2. 0x89[1:0] = 00 disables the undershoot limiter.
Regards,
Paul