input resistance of a trigger pin

[MichelM38]

Hi,

I wan't to use the stm32 as described in the video

https://youtu.be/dd5LaqmN8O0

https://controllerstech.com/stm32-timers-9-one-pulse-mode/

with the difference that I uses the trm4  and the input trigger is channel 1.

Operation is ok but applying the signal from a 3.3v signal generator lowers it to 2.3v! It's as if the input resistance of the trigger was a little too low. But I can't find anything about this. I applied this same signal to an input on capture, and there no problem, the signal remains at 3.3v.

Do you have any idea about the cause of this drop in signal?

Michel

 

 

[waclawek.jan]

Which STM32? What hardware? Which pin? How is that pin set in GPIO? What else is connected to that pin?

JW

[MichelM38]

It's the STM32F411 on the nucleo F411. The input pin is PB6, which is connected to nothing else but connectors CN10(17) and CN5(3)

MM

[MichelM38]

Th ouput is PB7

 

[waclawek.jan]

So, you say that you've connected generator output to PB6, and at that moment generator's output amplitude decreased from 3.3V to 2.3V?

If you hold the reset button, does the amplitude return to 3.3V?

JW

[MichelM38]

yes

[waclawek.jan]

That "yes" is to which one the two questions?

JW

[MichelM38]

Hi,

Sorry for the answer ;-(

So, yes, the generator's output decreased from 3.3v to 2.3v when I connect it on PB6.

And yes, the signal returns to 3.3v when I press the reset button or when I upload the program.

 

Michel

[waclawek.jan]

It then means that PB6 is set as output, either directly as GPIO Out, or indirectly as an AF which is set to output by the peripheral (e.g. TIM).

I don't know what exactly did you want to achieve and what did you do, the webpage you've linked to does not seem to mention PB6.

Read out and check/post content of TIM and relevant GPIO registers.

JW

[MichelM38]

As I said, the guy on the web page uses the timer 1  and I use the timer 4. So that' why you will not find PB6 on this site, but PA9(Time1 ch2)

And as i select the timer configurator ( .ioc) , the channel 1 is automaticly setting as en input.. And by the way, it works

T

And as I use it as a timer input, I can't setting it as a GPIO input

But I'm aggre, it seem like a pin setting as a ouput. Or may be some input resistance too low...

Michel

 

[AScha.3]

Just guessing : you drive a "big" signal directly to a cpu pin (no good idea anyway).

PB6 is your choosen pin, for trigger input - right ?

So when cpu running and digital input -> trigger connected + its input circuit might have protection diodes to gnd + vcc.

But on reset - "nothing" connected, pin is FT (5V tolerant) and only protection diode to gnd at pin; input impedance might be slightly higher, in giga-ohm range, so just any effect, if your signal generator has a Megaohm output impedance;

But now input signal at pin can be > 3vss ;

to check: connect a scope and look at the voltages .