Series resistor on serial and pwm output

[AvlKP]

I'm trying to learn by creating a flight controller. Found some reference schematics, and was wondering what is the use of these resistors? I tried to research it and guessed that it was series termination. But, from what I understand, series termination are supposed to be placed near driver. These resistors not only exist on TX but also RX. Can someone explain what are they for and how were the values chosen?

[PGPG]

I think all 220R resistors are to limit supply noise.
Any IC switching its output stage needs a current pulse from supply to reload the whole capacitance connected to its output. The faster IC the higher current pulse. When near the output you insert some R (I use 47..100R at all my outputs) these pulse at first moment is needed only to reload IC internal output capacity and reloading the connection wires capacity and receiver(s) input capacity is postponed in time making the pulse peak several times lower than when there is no R in serie.

PS.
As there are connectors than I suppose signals are inserted into cables (don't know how long). Cables (instead of tracks at PCB) like to be the noise emission source in devices. So the other function of these resistors is to limit signal bandwidth in these cables.
Values are chosen to not disturb normal circuit operation while make some noise reduction.