stm32l476rg with SN65HVD11P IC Transciever and AMT21 Encoder

[AaravD356]

Hi all,

I'm working on a project involving UART communication over RS-485 between an STM32 Nucleo board and a rotary encoder. I'd appreciate any advice or insights on whether my hardware and firmware setup looks correct, and what to check next to ensure reliable communication. 

Board: STM32 Nucleo-L476RG
Encoder: 6-pin rotary encoder with the following pinout:

• Pin 1: 5V

• Pin 2: B

• Pin 3: A

• Pin 4: GND

• Pin 5: MODE

• Pin 6: MCLR

RS-485 Transceiver: MAX485-compatible module

• RO (Receiver Out) → PA10 (USART1_RX)

• DI (Driver In) → PA9 (USART1_TX)

• RE (Receiver Enable) → PB3

• DE (Driver Enable) → PB4

• VCC: 3.3V (from Nucleo 3.3V)

• GND: common with Nucleo and encoder

• A ---> Encoder Pin A
• B ---> Enocder Pin B

PC Interface:

• I'm using a USB cable from the laptop to the Nucleo, which powers the board and also uploads code.

• USART2 is used for debug printouts via USB virtual COM port (seen in PuTTY).

• USART1 is used for RS-485 communication

• 

   

I believe my issue is in the software. How do I get communication?

Here are the datasheets:

Encoder: https://www.sameskydevices.com/product/resource/amt21.pdf

Transciever: https://www.ti.com/lit/ds/symlink/sn65hvd11.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1746316269944&ref_url=https%253A%252F%252Fwww.ti.com%252Fgeneral%252Fdocs%252Fsuppproductinfo.tsp%253FdistId%253D10%2526gotoUrl%253Dhttps%253A%252F%252Fwww.ti.com%252Flit%252Fgpn%252Fsn65hvd11

 

[Peter BENSCH]

Welcome @AaravD356, to the community!

At first glance, the hardware configuration looks OK. Do you have termination resistors on both sides of the RS-485 line?

We can only say something about the firmware once you have added at least a few lines of code.

Regards
/Peter