[SI-LIST] What is the difference between tDQSS, tDSS and tDSH

  • From: "Istvan Nagy" <buenos@xxxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Sun, 28 Mar 2010 15:17:46 +0100


The JESD79-xx Jedec standards specify three timing parameters for DDRx 
memory write clock-strobe timing:
tDQSS, tDSS and tDSH.
I understand the t_DQSS, that it makes shure that the strobe will arrive to 
the memory chip within a window relative to the clock, so we will latch the 
right data bit at the right time.
but what is the purpose of the other two parameters?
they seem to have a tighter value, so if they specify the same write 
clk-strobe matching, then the DQSS specification does not make sense, since 
the other two parameters already specified the same thing with a narrover 
anyway, are the DSS and DSH parameters input requirements or output 
guaranteed timings?
the jedec specs dont really make a difference between input requirements and 
output guaranteed timings in the explanations of the timing parameters. for 
example they say "setup time", but it can mean "input setup requirement" or 
"output worst-case guaranteed setup time", or just the actual setup time of 
a signal on a given point on the board.

Istvan Nagy

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