Hi everyone,
I’m having an issue with my setup and I’m running out of ideas. Maybe someone here has experienced the same thing.
Hardware
Board: BTT SKR Pro V1.2
Screen: BTT TFT50 (same behavior as TFT35)
Firmware: Latest Marlin (self-compiled)
Connection: 5-pin cable from TFT (RS232 port) → TFT port on SKR Pro
Problem
When using Touch Mode, the screen shows:
“No printer attached!”
However:
In Marlin mode (EXP1/EXP2) everything works perfectly
Motors move correctly
Firmware compiles without errors
Board responds normally
So the board itself is working — the issue is only in Touch mode (serial communication).
Wiring
I am using:
5-pin flat cable
RS232 port on the TFT
TFT port on the SKR Pro
I understand that despite being labeled RS232, this is actually TTL UART (3.3V).
EXP1 and EXP2 are not crossed. The machine works fine in Marlin mode.
Marlin Configuration Tested
Current configuration (compiles successfully):
C++
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#define SERIAL_PORT -1
#define BAUDRATE 115200
#define SERIAL_PORT_2 3
#define BAUDRATE_2 115200
I also tried:
C++
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#define SERIAL_PORT -1
#define SERIAL_PORT_2 0
Other combinations caused compilation errors like:
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template argument 2 is invalid
SerialOutputT {aka int}
With the current configuration, Marlin compiles fine.
TFT config.ini
In config.ini:
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serial_port:P1:6 P2:0 P3:0 P4:0
Where:
P1:6 = 115200 baudrate
I have also tested:
250000 baud
Matching baudrates on both sides
Reflashing TFT firmware
TFT Settings
Touch → Settings → Connection → Ports:
P1 (Printer) enabled
115200 selected
Still shows:
No printer attached!
Strange Behavior
If I unplug the 5-pin cable completely:
The TFT still shows activity under:
TX gcode bytes
Scan rate
So it seems like the TFT is transmitting, but not receiving anything from the board.
What I’ve Already Checked
Cable is straight (not crossed)
Baudrates match
TFT firmware updated
Marlin recompiled from scratch
Board works in Marlin mode
Connected to TFT port (not EXP1/EXP2)
Questions
Is SERIAL_PORT_2 3 correct for SKR Pro V1.2 TFT port?
Could the TFT port be mapped to a different UART?
Could USB (-1) be conflicting?
Is there something that must be enabled in pins_BTT_SKR_PRO_common.h?
Does anyone have this exact setup working in Touch mode?
Goal
I want Touch mode to properly connect and control the machine instead of showing “No printer attached”.
If someone has this board + TFT working, I would really appreciate if you could share your exact:
SERIAL_PORT
SERIAL_PORT_2
BAUDRATE
BAUDRATE_2
Marlin mode works perfectly — only Touch mode cannot communicate.
Thanks in advance 