关于USART TTL电压幅值衰减问题

[Albert_Meng]

最近使用STM32F429BIT6芯片作为MCU开发一款物联网集中控制器，作为总的网关将Lora、RS485、WiFi等通信终端（灯具）信息透传至以太网络，与服务器进行数据交互。

近期使用期间遇到以下问题：在使用USART6（PC6、PC7）、USART7（PF6、PF7）与Lora、WiFi模组进行通信时，功能正常，接口电路如图：

为了增加集中控制器带载量，我们需要增加Lora模组进行扩容，再此期间发现异常，在使用USART2（PD5、PD6）、USART3（PB10、PC11）与模组通信时，电平幅度衰减，导致通信异常。

采用示波器抓取波形，在不连接Lora模组转接板时，USART2（PD5、PD6）、USART3（PB10、PC11）发送波形幅值正常0~3.3V，在连接Lora、WiFi模组转接板时，波形幅值异常，如上图：

另外可查看附件录制波形小视频。

在使用安信可USB转串口工具与电脑连接时，USART2（PD5、PD6）、USART3（PB10、PC11）、USART6（PC6、PC7）、USART7（PF6、PF7）钧能正常收发数据，

串口工具接收数据如图：

求教USART2（PD5、PD6）、USART3（PB10、PC11）与USART6（PC6、PC7）、USART7（PF6、PF7）之间存在哪些差异？或者硬件设计上如何做放大隔离？

[Tesla DeLorean]

Like you're driving signals into the wrong pins, there's a short, or the grounds aren't properly/effectively bonded.

[Albert_Meng]

能给出更详细的解释吗？

[Tesla DeLorean]

>>Can you give a more detailed explanation?

Not really, you've not really presented your entire circuit or wiring.

The inter-modulation you're showing is likely due to driver pins being shorted together, or having some conductive path through resistors. Perhaps pull-up / pull-down resistors to a floating node, rather than being one of the rails.

Or you have ineffectual grounding in the system.

Hard to tell from here, you're going to have to debug your own circuits, and think about possible causes.

I don't see you configuring multiple UARTs on the STM32 side will do this.

Check the pin configurations, especially those presenting the signals shown.

[Albert_Meng]

找到原因了，是tx和rx原理图出反了😂