STM34L431 UART receive on Pin PB10, Pin always high signal

[M.Harms]

Hello,

I have a problem with the Controller. For some time the Uart is working fine. Than the UART receive Interrupt is not generated anymore.

I check the working pcb with the debugger and the scope. I see there is no Signal on the pin. The uart from the controller is connected to my PC with  H11L1 opto Isolator in the RX and TX line. So I check the Isolator and see a signal on the LED of the Isolator. The PC send out data but the signal ends on the isolator. So I tried the Isolator on a reference board and everything works fine. I take a other Isolator and test it with my reference board it works also.

Both isolators give me the same result on my working pcb. It looks like the pin PB10 is internally connected to 3,3V and always high.

I do a little experiment and take a wire with GND signal and touch the output of the isolator with this. The Debugger shows me an RX interrupt, the moment I pull down the pin. 

The internal Pull Up where checked, also the alternativ function registers. 

Have anyone a idea why the pin is always high?

[waclawek.jan · Accepted solution]

Show us relevant part of schematics and show measured signals on individual pins of H11L1 (including those you assume to be at a given potential, e.g. ground - measure continuity, assume bad solder joints).

JW

[AScha.3 · Accepted solution]

>Than the UART receive Interrupt is not generated anymore.

so- before it was working. you didnt change program ? then you damaged chip - possibly.

can you try another chip or board ?

[M.Harms]

Yes it was ok for some time. Since the problem with the Uart occured I reprogram the chip again, because I was thinking of a mistake there. But it dosen´t change something. Also I reprogram the chip again toput the debug version of the software into the chip.

The same software is working on around 30 other devices. 

[M.Harms]

Green is the TX signal from the chip.

Yellow the RX from the chip.

Scope 12 is the isolator side of the chip.

scope 13 the PC side.

[waclawek.jan]

It may be damaged H11L1, or any connection to it (series resistor to the diode, bad solder joints).

JW

[M.Harms]

The H11L1 is ok. On the reference pcb the isolator works fine.

It looks to me like, the controller pin internally connected to 3,3V