This could be a better approach:
stty -F /dev/ttyUSB0 115200 raw -echo #CONFIGURE SERIAL PORT
exec 3</dev/ttyUSB0 #REDIRECT SERIAL OUTPUT TO FD 3
cat <&3 > /tmp/ttyDump.dat & #REDIRECT SERIAL OUTPUT TO FILE
PID=$! #SAVE PID TO KILL CAT
echo "R" > /dev/ttyUSB0 #SEND COMMAND STRING TO SERIAL PORT
sleep 0.2s #WAIT FOR RESPONSE
kill $PID #KILL CAT PROCESS
wait $PID 2>/dev/null #SUPRESS "Terminated" output
exec 3<&- #FREE FD 3
cat /tmp/ttyDump.dat #DUMP CAPTURED DATA
stty -F /dev/ttyUSB0 115200 raw -echo #CONFIGURE SERIAL PORT
exec 3</dev/ttyUSB0 #REDIRECT SERIAL OUTPUT TO FD 3
cat <&3 > /tmp/ttyDump.dat & #REDIRECT SERIAL OUTPUT TO FILE
PID=$! #SAVE PID TO KILL CAT
echo "R" > /dev/ttyUSB0 #SEND COMMAND STRING TO SERIAL PORT
sleep 0.2s #WAIT FOR RESPONSE
kill $PID #KILL CAT PROCESS
wait $PID 2>/dev/null #SUPRESS "Terminated" output
exec 3<&- #FREE FD 3
cat /tmp/ttyDump.dat #DUMP CAPTURED DATA