BTT TFT70 V3.0 refusing to connect to BTT GTR V1.0 with latest firmware

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    First things first, yes, i have made sure many times by now that the screen is connected correctly to the controller. the screen turns on and marlin is updated to the latest release (2.0.8) The serial port 1 is configured as -1 and serial port 2 is configured as 3. the baudrate is set at 250000 and i’ve tried 115200 and 19200 with the same results. The EXP ribbon cables for marlin mode are disconnected, so only the 5 pin serial cable is connected.

    The issue is as follows: the screen reports “no printer attached” even though i have full control over the printer. i can move all of the axis, control the fan speeds and send and receive any Gcode commands through the terminal menu (like M503, M115, M48 etc.) This confirms that there is in fact data being sent and received. but the screen still reports that it’s not connected and the coordinates don’t update when i move an axis.
    I’ve made sure that all of the recommended settings listed in the config.ini are enabled in the marlin build.

    This problem started when i upgraded the firmware of the screen to the latest version (3.0.27) downloaded from the official github. unfortunately i’ve found that its impossible to revert back to the stock firmware as there is no previous version of the firmware that supports the screen. even though i’m confident that the original firmware was an older version (it used a different theme for the status screen live icons).

    This makes it impossible for me to use the product before this issue is fixed!

    To make this issue even more confusing: i have (limited) access to another BTT GTR V1.0 and a BTT TFT35 V3.0 with their communication configured identically. connecting the second controller to the TFT70 works, connecting the controller to the TFT35 works. but together they refuse.

    is there anything that could indicate communication issues if i am able to run a M503 command from the screen’s terminal?


    Update: This issue has been (sort of) resolved. turns out that the display requires an extruder axis to be defined to consider the printer connected. had to add a fake extruder axis on unused pins that normally connects to the M5 expansion board. The screen works as expected but the controller is of course spitting out errors on boot because there is no driver connected to it’s specified pins.

    If anyone actually reads this i hope it may help you out.
    The core of this issue lies somewhere in the code that determines if a printer is connected but unfortunately i was unable to find said code to be able to modify it. Any pointers in the right direction would be awesome.

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