Hello all,
I am new to HIGH Speed PCB Design and need inputs on routing the pinout for STM32H750XB With SDRAM IS42S32400F-7TLI-TR, the EVK Available from STM have series resistances in between the RAM and MCU but in some places people are using direct connections in there dev boards . So which method is correct to route the interface between these two.

 

You need to understand the purpose of the series resistors. Some people can get it working fine without additional resistors.

Every piece of wire on a circuit board is a transmission line and suffers from transmission line effects which result in signal degradation. These effects are dependent on many parameters:

1. frequency of signals
2. length of the wire
3. impedance of the wire
4. stray capacitance and inductance

Every connection has a characteristic impedance. In order to minimize reflections on the wire, the source driver should have an output impedance that matches that of the transmission line.

This is called series termination.




Parallel termination requires that the receiving end of the transmission line be terminated.



You may choose to ignore proper transmission line termination at your peril.

 

As usual, it depends.

 

For things like higher speed SPI, on normal digital ports without impedance specifications, series termination should be used for off board interconnects to improve signal integrity.

https://forum.allaboutcircuits.com/threads/maximum-via-stub-length.197607/post-1869871

The normal board to board wiring interconnect wiring with no specific impedance.

I'm scoping the 15MHz SPI clock signal to the GLCD display. Yellow: at the board connector, Green: at the display connector.

The signal integrity improvement solution at the display connector end is a simple series resistor as seen in this GLCD prototype board.
It will run a 15MHz without the resistor but I wanted a better signal at the display with a 30MHz clock.