When serializer and deserializer have different HIM setting, can it cause problems?
The default reverse control channel (deserializer to serializer) in all GMSL1 devices uses NRZ coding, where data transitions are sent as a 1us positive pulse for a 0 to 1 transition and a negative 1us pulse for a 1 to 0 transition. Data is also coded for transmission. On reception the height and duration of the pulses is checked, the alternating polarity is checked, and coding integrity is checked
Devices in the MAX92xx series starting with MAX9275 and all MAX967xx devices have high immunity mode (HIM) as an option. HIM sends two pulses instead of one. A positive pulse followed by a negative one for a 0 to 1 transition, and a negative pulse followed by a positive one for a 1 to 0 transition. This allows additional checking of the actual pulses as the seperation of the pulse pair can be verified and single noise pulses will be rejected. This is done to reduce the error rate on the reverse control channel. When available, this option should always be used.
There are some cases (like 2 different types of camera used for the same system) where one device will not know on power up whether the connected device is using HIM or not and so it can initially try to communicate without HIM and then with HIM. This prompts the question: Will this cause problems? For instance, will the HIM part interpret a non-HIM command incorrectly and act on it, causing a malfunction.
The answer is no. Using non-HIM communication first, an HIM part will reject non-HIM data in both the pulse and coding checking stages. Therefore a system using a mix of devices which power up as non-HIM and devices which power up as HIM is possible without issue.
