10.3.1.6.4. RLDRAM 3 Data, DM and QVLD Signals
Intel® devices use dedicated DQS phase-shift circuitry to shift the incoming QK signal during reads and use a PLL to center-align the DK and DK# signals with respect to the DQ signals during writes.
For RLDRAM 3, data mask (DM) pins are used only during a write. The memory controller drives the DM signal low when the write is valid and drives it high to mask the DQ signals.
For RLDRAM 3, there are two DM pins per memory device. DM0 is used to mask the lower byte for the x18 device and (DQ[8:0],DQ[26:18]) for the x36 device. DM1 is used to mask the upper byte for the x18 device and (DQ[17:9], DQ[35:27]) for the x36 device.
The DM timing requirements at the input to the memory device are identical to those for DQ data. The DDR registers, clocked by the write clock, create the DM signals. This reduces any skew between the DQ and DM signals.
The RLDRAM 3 device's setup time (tDS) and hold (tDH) time for the write DQ and DM pins are relative to the edges of the DK or DK# clocks. The DK and DK# signals are generated on the positive edge of system clock, so that the positive edge of CK or CK# is aligned with the positive edge of DK or DK# respectively to meet the tCKDK requirement. The DQ and DM signals are clocked using a shifted clock so that the edges of DK or DK# are center-aligned with respect to the DQ and DM signals when they arrive at the RLDRAM 3 device.
The clocks, data, and DM board trace lengths should be tightly matched to minimize the skew in the arrival time of these signals.
RLDRAM 3 devices also have a QVLD pin indicating valid read data. The QVLD signal is edge-aligned with QK or QK# and is high approximately half a clock cycle before data is output from the memory.
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