Hynix DDR2 Single-Ended DQS Questions

I have a Linux system using a PowerPC 405EX processor. For cost reasons, we used a 200 pin DDR2 SO_DIMM rather than solder the memory to the PCB. This has been working fine with DIMMs built using either Micron or Samsung DRAM. However, we bought some additional Crucial modules that were built with Hynix memory. These do not work. Often the PowerPC will hand during the boot cycle. Otherwise, it will crash after getting to a prompt. I can force a crash by running a memory test after boot. Usually the memory test fails with bad data in a single byte. I can run the same memory test on Micron or Samsung DRAM repeatedly and never get a fail. The PCBs appear to be the same JEDEC design, so they only difference is the DRAM. (The SPD data is not used in this PPC 405EX setup.)

I have a 460EX Canyonlands Dev Board that will accept the same DIMM. The problem Hynix DIMMs boot fine in the Dev Board. The difference in the two processors is that the 460EX offer differential DQS and the 405EX only offers single-ended DQS. On my board, the unused DQS~ lines are tied to ground via 1K ohm resistors. I reduced these to 20 ohms, but it did not improve anything.

Has anyone experienced single-ended DQS problems with Hynix DDR2 DRAMS?

Hi, guess you have configured the DRAM to work with Single Ended DQS.
Nevertheless I would try to terminate the DQSb at the midlevel (VTT) instead of GND.
Have you tried this ?

Hermann

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