Need write some code and run it ?
Or add some code into the firmWare source code ,compile it & refresh it into the machine ?
The default content cannot be modified, it is fixed in the MCU firmware. We provide configuration, you can hide/show the default page, provide a custom page, you can display your own information.
if I wanna import display some customized dynamic content instead of static ‘test msg’ , how to do that ?
for example:
I wanna display the current GPS position data (Lontitude=129 Nor,Latitude=81 East … ) on that small LED screen while I inserted a USB GPS antenna into the USB2.0 port of the machine.
Can’t modify MCU firmware?? 
You do not need to modify the MCU firmware to display your dynamic information. This requires you to write a shell script to obtain GPS information regularly, and replace the key value of content with your own information.
echo {"display_mask": "1f", "custom_en": "1", "content": " your GPS info "} >/tmp/mcu_message &&killall -17 e750-mcu
Need to add escape character
echo {\"display_mask\": \"1f\", \"custom_en\": \"1\", \"content\": \" your GPS info \"} >/tmp/mcu_message &&killall -17 e750-mcu
Need write the dynamic GPS position stream data into the file ‘mcu_message’ continuously ?
Yes, you can update the data regularly according to your needs, with an interval of 60s, 30s or other