nano-s uart not working for tmc2209

[pznamenskii]

hi.
I am trying to install tmc2209 into E1 socket on nano-s board and connect via uart (4th pin on tmc2209 (PDN) as TX to PC14 via 1k resistor and as RX directly to PC15:

Marlin/src/pins/stm32f4/pins_MKS_ROBIN_NANO_V1_3_F4.h:
#define E0_SERIAL_TX_PIN                  PC14
#define E0_SERIAL_RX_PIN                  PC15
#define TMC_BAUD_RATE 19200

Marlin/Configuration_adv.h:
#define E0_SLAVE_ADDRESS 0
#define E0_CURRENT      550
#define E0_MICROSTEPS    32
#define STEALTHCHOP_E
#define MONITOR_DRIVER_STATUS
#define TMC_DEBUG

Marlin/Configuration.h:
#define MOTHERBOARD BOARD_MKS_ROBIN_NANO_V1_3_F4
#define E0_DRIVER_TYPE TMC2209

driver is not seen with the below M122 S0 response:

09:52:10.380 : Driver registers:
09:52:10.380 : E	0x00:00:00:00	 Bad response!
09:52:10.381 : Testing E connection... Error: All LOW

[mks-viva]

You only need to use an IO to connect to the PDN_UART pin of TMC2209, you can refer to：https://www.youtube.com/watch?v=7ShcFKXrVHo

[pznamenskii]

You only need to use an IO to connect to the PDN_UART pin of TMC2209, you can refer to：https://www.youtube.com/watch?v=7ShcFKXrVHo

doing so will likely damage your board: nano-s board has MS3 hardwired with a 0Ohm resistor and until your remove it, UART pin on driver will get voltage as in a non-UART configuration. there is no way to connect UART without soldering out that resistor which is an extremely inconvenient board design.

[mks-viva]

TMC2209 compatible with 3.3V and 5V

[pznamenskii]

TMC2209 compatible with 3.3V and 5V

it is, but UART will not work until you remove this resistor

by not removing it, you load 3.3 or 5V to the pin on the board you chose to use as UART line, i.e. PC14 - this may damage the board

[mks-viva]

You need remove it, because it is use to microstep settings for plug driver.