Why in the STM32H7445I-DISCO Highspeed path length we only consider the length between the resistance and the ram, but not the length of the resistance to the MCU (for example the netRXX to the MCU pin)? So we don't consider the full path between MCU-RAM?

[ANaud.1]

I am a student starting in highspeed tuning...

[TDK]

> Why in the STM32H7445I-DISCO Highspeed path length we only consider the length between the resistance and the ram, but not the length of the resistance to the MCU (for example the netRXX to the MCU pin)? So we don't consider the full path between MCU-RAM?

What is the "the length between the resistance and the ram"?

Typically the bond wires inside the mcu and RAM are insignificant in the overall scheme, if that's the question. Keeping trace lengths about equal is sufficient in the tens of MHz range.

[ANaud.1]

Hi and thanks for your answer.

Here I am not talking about the internal resistance. I am really talking about the resistance we put (33ohms) in the entry of the MCU pins. The length between this resistance and the MCU is not calculate in the disco PCB, only the length that go between the resistance and the RAM is. I don't really know how to explain much at this point, I am sorry...

You can go see that link: https://www.st.com/en/evaluation-tools/stm32h745i-disco.html#cad-resources and check for the schematic at the bottom. In these schematic, you can go to sheet 3 (MicroController IOs) and check the 33 ohms resistance (like R108). I am talking about these one.

Thanks,