In addition to dkfire's comment:
As you have written tho microcontroller part you should also show the relevant code which translates the ADC reading to the serial port writing in this microcontroller!
This way it would be much easier to suggest a VISARead implementation - in addition to "get rid of BytesAtPort" and "use a loop"!
Best regards,
GerdW

using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019