1a2m3
UDIMM DDR4 16GB not recognized
Issue Description: I designed a PCB based on your reference schematic. The DDR5 memory (8GB-32GB) works perfectly. However, with DDR4 memory:
8GB modules are detected correctly by SPD-RW (SPD read/write tool).
16GB modules (tested with Kingston 16GB 3200MHz) show "Nothing found".
Observations:
DDR5 compatibility is flawless.
DDR4 16GB modules fail detection while 8GB works.
Request: Have you encountered similar DDR4 capacity detection issues? Could this relate to PCB design constraints (e.g., signal integrity, addressing, or SPD differences between DDR4/DDR5)? Any insights would be greatly appreciated.
@EFTNice If you want to share your pcb design files I can try to debug your issue.
There are many many many VSS pins required on a DDR4 DIMM interface. There's no rule saying that one of the couple of specific pins you've chosen to connect to GND has to be the return path for VDDSPD, only that the dozens of VSS pins together constitute the return path. DIMM makers are thus very likely free to do whatever fits best. It is most likely not a memory module size issue, just a DIMM-PCB sourcing issue.
I guess you should try connecting all the VSS pins to ground. Sounds dumb and cumbersome, I know. Or to start small, try getting the proximal VSS pins (283, 138) connected first.
