We've been having some internal discussions on DDR tQH/tQHS that I'm hoping some (memory) experts can provide some insight on. Some background: DDR2 specs provide a tQHS number (data hold from next DQS strobe). From this one can derive a tQH number (DQS to first DQ invalid) using the following formula (ignoring the inclusion of jitter for this discussion): tQH = tHP - tQHS For DDR3 the specs provide tQH (expressed as a percentage of tCK). Though not explicitly stated in the specs I would (dangerous word here) "presume" one could use the same formula above to derive a tQHS value if one were so inclined. Here's the question: what happens when a DDR device is operated at a frequency that's slower than it's bin rating? For DDR2 tQHS remains constant and tQH (expressed as a percentage of tCK) varies. Following strict interpretation of the DDR3 spec it's tQH (expressed as a percentage of tCK) that remains constant and tQHS that varies, the opposite of DDR2. I am skeptical of this for DDR3. I would expect that it's really tQHS which remains constant across different operating frequencies for a given speed grade, but am not familiar enough with DDR internal implementation to be certain. Can anyone shed some insight into this apparent discrepancy? Thanks, -- Conrad Herse Alcatel-Lucent ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu