GPIO output voltage

[SIDRI.1]

Hi,

I would like to design a debug LEDs for UART/I2C communication (STM32F103), 

the purpose is just to see wether the communication is working or not, through a LED, here is my schematic, 

My questions are :

1) what is exactly the output voltage on Tx and SDA pins , when no communication is present. (idle state) ?

2) what is the VoL and VoH for GPIO's ?

i have tried to measure the voltage in Tx pin ( during communcation and during idle state), but it is always about 3.3v . 

Any recommendation ? 

if idle state is 3.3v i should modify my schematic.

Thank you .

[Tesla DeLorean]

The I2C SDA/SCL and USART TX pin are normally HIGH, ie 3.0 - 3.3V depending on implementation, supplies etc.

The low time for any other them is likely below the eye's ability to respond, which I why people typically use scopes to view fast signals

2) Should be in the Data Sheet

[SIDRI.1]

Okay thank you for your response ,

here is logical level for gpios (both TTL and CMOS ports) i get it !

[Ozone]

The GPIO output voltage might not suffice to drive a MOSFET.

Check with the transistor's datasheet.

[SIDRI.1]

Hi,

I'm using BSS138BK mosfet for GPIO's, with Vgsth min = 0.48v and Vgsth max = 1.6v, the GPIO output voltage is above vgsth when MCU is supplied with 3.3v , so i think it can drive the mosfet's in fully open mode