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I'm trying to use software UART for TMC2209 steppers on a BigTreeTech v1.2 and apply that to my Robin Nano v.1.1 using Klipper firmware.

I declared a different pin for every driver and I edit my printer.cfg in this way:

[tmc2209 stepper_x]
uart_pin: PA10
run_current:  0.75
hold_current: 0.4
stealthchop_threshold: 9999
interpolate: true

[tmc2209 stepper_y]
uart_pin: PA9
run_current:  0.75
hold_current: 0.4
stealthchop_threshold: 9999
interpolate: true


[tmc2209 stepper_z]
uart_pin: PC7
run_current:  0.75
hold_current: 0.4
stealthchop_threshold: 1
interpolate: true


[tmc2209 extruder]
uart_pin: PC13
run_current: 0.3
stealthchop_threshold: 1
interpolate: true

I watched this video

enter image description here

But I have this error:

Unable to read TMC UART 'extruder' register IFCNT

Why is this happening?

0scar
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Borja
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1 Answers1

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I had the same issue. In general, that means that the pins you specified doesn't work.

"I declared a different pin for every driver": you don't need just "different pins", you need the CORRECT pins. Check if you specified the correct ones: below the SKR the pins are labelled.

And then check that the TMC module has the UART pin(s) (there are two) are connected to the chip! the TMC modules often are sold with three empty pads on the lower side of the PCB. The central one goes to the chip, then each other pad goes to one pin. You need to bridge with solder the central one and the pad for the pin you want to use.

In the following image you can (barely) see that the central pad near the red line is bridged with the upper one.

enter image description here

Also, for the extruder the stealthchop threshold should be 0, not 1! you don't want stealthchop for the extruder.

FarO
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