2021-02-17 11:56 AM
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 .
2021-02-17 12:03 PM
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
2021-02-18 02:53 AM
Okay thank you for your response ,
here is logical level for gpios (both TTL and CMOS ports) i get it !
2021-02-18 03:19 AM
The GPIO output voltage might not suffice to drive a MOSFET.
Check with the transistor's datasheet.
2021-02-18 07:14 AM
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