Timeout when receiving modbus data

[octarudin]

Hello, I don't know where my mistake is. Plase help me. Below is my specification.

• STM32F411CE 100Mhz PLL HSE Clock.
• Wiring diagram, logic analyzer screenshot, and source code attached.
• USART1 (PA9 as USART1_TX and PA10 as USART1_RX) just for printf / transmit serial data to PC.
• USART2 (PA2 as USART2_TX and PA3 as USART2_RX) for communicating with modbus devices (in this case PZEM-016 and XY-MD02).
• Not using USART Interrupt.
• Slave ID=1, Start address to read=0, Quantity=10 for PZEM-016.
• Slave ID=2, Start address to read=1, Quantity=2 for XY-MD02.
• Reading Input Register (FC 04) for those modbus devices.
• I use TTL-RS485 module.

The problem:
this code always get timeout when receive modbus data, but it can write modbus frame successfully.

nmbs_error err = nmbs_read_input_registers(&nmbs, 1, 10, &r_reg)
the err value always NMBS_ERROR_TIMEOUT.

Source Code in txt, generated by STM32CubeMX
source code.txt

Wiring diagram

Serial monitor output / USART1

Logic analyzer on TTL-RS485 Module

Thanks for helping me.

[donghoonpark]

Hi there.
Your code seems have no flaw. I already have tested nanomodbus with same environment.

Have you tested your system with verified tools such as modbus poll or qmodbus?
Some modbus slaves do not give response if address is not in valid range. You need to check the exact region to read first.
It also would be helpful to test your system with verified slave software such as modbus_slave

I hope you solve the problem well.