Nick_Pyner:
Quite likely a rational reason. Some explanation of why you have these restrictions on what you can and cannot do might be in order, and most particularly, who imposed them.
I have this constraint as I have a limited area for our system. I will use two microcontrollers that are compatible with arduino library. Thus, I will have no more space for an additional component, like a multiplexer.
Moreover, I cannot transmit the data to a single board as the power consumption of this action will be higher than connecting directly to an sd.
As the microcontrollers are not very powerful I need to do different things on the two boards, thus, sending the data to a board will stop the computation in this board.
I can connect two more serials for handling the locking, as adding some cable will not be a problem.
Thank you.