A9 and M4 serial communication problem from Bash

I want to send a command to Arduino to trigger data aquisition and read the results (two values).
A first test with cu works as expected (see first image). Building a shell script was not successful.
Using stty to set the baud rate was not accepted. stty /dev/ttyMCC -a shows a baud rate of 38400. I think this is wrong. Default should be 115200. The cooked option was not accepted, too. Furthermore calling read the script hangs (see second image).
Do you have any hint what's wrong here?

Code:

#!/bin/bash

set -ex

#stty -F /dev/ttyMCC 115200 cooked

while true; do
  echo "AAA" > /dev/ttyMCC
  read -r ID < /dev/ttyMCC
  echo $ID
done 

 

The following script worked on a UDOO Quad. The Arduino was connected via ttymxc3.
For UDOO NEO the program hangs. stty is commented because it fails too.

Code:

#!/bin/bash

#Port settings
#stty -F /dev/ttyMCC raw speed 115200

while  :
do
  echo 1 > /dev/ttyMCC
  read -r CMD < /dev/ttyMCC
  echo $CMD
  sleep 1
done

 

It's a known issue. we're looking for a way to solve it.