Is internal pull up the same as external pull up resistor.

[MNapi]

for example IC2 needs pull up resistor on the board but there is internal pull up options for pins.

I wonder if this is the same. So by setting internal pull up you can skip the pull up resistors on the board. I know that NRST pin has internal pull up resistor.

 

[KnarfB]

No. internal pull-up has a much higher resistance(~40 kOhm? check data sheet) than a typical I2C pull-up (4,7 kOhm, depending on your setup).

hth

KnarfB

[MNapi]

I followed example from CubeMX to connect 2 Nucleo boards F446, using I2C and they use internal pull up and it does work. I wonder if I can use for example internal pull up for example for SDMMC.

[DTomi.1]

What was the clock speed used in this example?

Keep in mind that this 40 kΩ weak pull-up in combination with line and input capacitances is forming a low-pass filter.

So it depends how long and wide your PCB traces are (rule of thumb is 1 pF/cm length for 0.2mm trace width and 0.2mm height above plane - prepreg thickness) and how many slave devices you have on the bus (I/O pad capacitance - around 5 pF per pad).

For example a 10 cm PCB trace (10 pF) + input capacitance (5 pF) = 15 pF

which gives a rise-time of 1.3 us so not good at all for anything above around 500 kHz.

[Tesla DeLorean]

The F446 is an MCU, retagged into the proper forum.

MPU = STM32MP1 LINUX, et al