GS4576C09/18/36L
Read
Read data transfers are launched with a Read command, as shown below. Read Addresses must provided with the Read command.
Each beat of a Read data transfer is edge-aligned with the QKx signals. After a programmable Read Latency, data is available at the
outputs. One half clock cycle prior to valid data on the read bus, the data valid signal (QVLD) is driven High. QVLD is also edge-
aligned with the QKx signals. The QK clocks are free-running.
The skew between QK and the crossing point of CK is specified as tCKQK. tQKQ0 is the skew between QK0 and the last valid data
edge generated at the DQ signals associated with QK0 (tQKQ0 is referenced to DQ0–DQ17 for the x36 configuration and DQ0–DQ8
for the x18 configuration). tQKQ1 is the skew between QK1 and the last valid data edge generated at the DQ signals associated with
QK1 (tQKQ1 is referenced to DQ18–DQ35 for the x36 and DQ9–DQ17 for the x18 configuration). tQKQx is derived at each QKx
clock edge and is not cumulative over time. tQKQ is defined as the skew between either QK differential pair and any output data edge.
At the end of a burst transfer, assuming no other commands have been initiated, output data (DQ) will go High-Z. The QVLD signal
transitions Low on the beat of a Read burst. Note that if CK/CK violates the V
specification while a Read burst is occurring,
ID(DC)
QVLD remains High until a dummy Read command is issued. Back-to-back Read commands are possible, producing a continuous
flow of output data.
The data valid window specification is referenced to QK transitions and is defined as: tQHP – (tQKQ [MAX] + |tQKQ [MIN]|). See the
Read Data Valid Window section for illustration.
Any Read transfer may be followed by a subsequent Write command. The Read-to-Write timing diagram illustrates the timing
requirements for a Read followed by a Write. Some systems having long line lengths or severe skews may need additional NOP cycles
inserted between Read and Write commands to prevent data bus contention.
Read Command
CK
CK
CS
WE
REF
Addr
A
BA(2:0)
BA
Rev: 1.04 11/2013
24/62
© 2011, GSI Technology
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
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