Thank you for suggestions of other chips,
but one of the main requirements is code compatibility.
Having written and proven the software on a RasPi, I would wish Raspbian and my code to run (ideally) unchanged on a Micro-Pi.
Too much to hope for?
Did you ever get the Moxa Uport 1110 driver working?I will add another device to the mix tomorrow: a Moxa Uport 1110.