System Workbench for STM32

Posted by steven12 at 14:35

Hi everyone,

I’m looking into how to handle Modbus RTU communication on an STM32 using the HAL library and an RS-485 transceiver, and I have a question about receiving complete frames reliably.

One thing I’m trying to understand is the difference between using UART IDLE detection and a timer to detect the end of a Modbus RTU frame. Since IDLE detection can trigger after roughly one character time, it may not be enough to confirm the required 3.5-character silence between frames.

For example, at 9600 baud with 8E1 configuration, would you normally use a hardware timer that restarts whenever a byte arrives, or is there a better approach using the STM32 UART peripheral?

I’ve been reading some STM32 and RS-485 implementation notes, including a PCBCool technical guide, and I’m interested in how developers handle this in real projects.

A few things I’d like to understand:

• Do you prefer UART interrupts or DMA for receiving Modbus RTU frames?
• How do you reliably detect the end of a frame?
• Are there any common pitfalls with UART IDLE detection or receiver timeout configuration on STM32?

I’d appreciate hearing how others have implemented this, especially on STM32F4 or similar devices.

Thanks!