STM32WB55 Nucleo --- general question on A/D scan conversion??

[SWenn.1]

When A/D is set to scan thru a sequence of channels can a single external trigger allow you to go thru the whole sequence or do I need a trigger for each of the channels in the sequence??

Been struggling with this for a while and I have some bare bones code....It looks like I need a trigger for every channel in the sequence

Thank you