TMC2208 Standalone Mode: Just don't do it.
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TMC2208 UART Mode: VREF is set to a max value here, but Klipper decides what to actually use based on the current you specify in printer.cfg Note: in Klipper you do not need to add the second pin with the resistor. (tx_pin) You may use one pin on the board, the UART_Pin
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Here is an Instructables page for those who want everything in print.
{% embed url="https://www.instructables.com/id/UART-This-Serial-Control-of-Stepper-Motors-With-th/" %}