1.1.10. QDR IV SRAM Clock Signals
The three QDR IV differential clocks are as follows:
- Address and Command Input Clocks CK and CK#
- Data Input Clocks DKx and DKx#, where x can be A or B, referring to the respective ports
- Data Output Clocks, QKx and QKx#, where x can be A or B, referring to the respective ports
QDR IV SRAM devices have two independent bidirectional data ports, Port A and Port B, to support concurrent read/write transactions on both ports. These data ports are controlled by a common address port clocked by CK and CK# in double data rate. There is one pair of CK and CK# pins per QDR IV SRAM device.
DKx and DKx# samples the DQx inputs on both rising and falling edges. Similarly, QKx and QKx# samples the DQx outputs on both rising and falling edges.
QDR IV SRAM devices employ two sets of free running differential clocks to accompany the data. The DKx and DKx# clocks are the differential input data clocks used during writes. The QKx and QKx# clocks are the output data clocks used during reads. Each pair of DKx and DKx#, or QKx and QKx# clocks are associated with either 9 or 18 data bits.
The polarity of the QKB and QKB# pins in the Intel® FPGA external memory interface IP was swapped with respect to the polarity of the differential input buffer on the FPGA. In other words, the QKB pins on the memory side must be connected to the negative pins of the input buffers on the FPGA side, and the QKB# pins on the memory side must be connected to the positive pins of the input buffers on the FPGA side. Notice that the port names at the top-level of the IP already reflect this swap (that is, mem_qkb is assigned to the negative buffer leg, and mem_qkb_n is assigned to the positive buffer leg).
QDR IV SRAM devices are available in x18 and x36 bus width configurations. The exact clock-data relationships are as follows:
- For ×18 data bus width configuration, there are 9 data bits associated with each pair of write and read clocks. So, there are two pairs of DKx and DKx# pins and two pairs of QKx or QKx# pins.
- For ×36 data bus width configuration, there are 18 data bits associated with each pair of write and read clocks. So, there are two pairs of DKx and DKx# pins and two pairs of QKx or QKx# pins.
There are tCKDK timing requirements for skew between CK and DKx or CK# and DKx# .Similarly, there are tCKQK timing requirements for skew between CK and QKx or CK# and QKx# .
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