OCTO SPI output impedance on H7-series

[Southbranch]

I have swapped from a custom PCB-board with a 6-layer stack using a STM32H725IGKB, to another custom board with a 4-layer stack using STM32H723ZGT6 (simpler package).

I am using an external OCTO SPI on both boards, but I have R/W errors with the 4-layer board.

Both boards are routed with 50 ohms impedance and uses 33 ohms series resistors for the OCTO SPI.

I am wondering if the output impedance is the same for these two H7-devices?

[Jonshill]

Here is a safer, very plain version you can post:

The OCTOSPI output impedance is the same on STM32H725 and STM32H723, so the MCU change is unlikely to be the cause.

The read and write errors on the 4 layer board are more likely due to signal integrity or return path differences, such as reference planes, vias, length matching, or power and ground layout, even with 50 ohm routing and 33 ohm series resistors.