220.127.116.11. DLL Phase-Shift
The DLL can shift the incoming DQS signals by 0° or 90°. The shifted DQS signal is then used as the clock for the DQ IOE input registers, depending on the number of DQS delay chains used.
All DQS pins referenced to the same DLL, can have their input signal phase shifted by a different degree amount but all must be referenced at one particular frequency. However, not all phase-shift combinations are supported. The phase shifts on the DQS pins referenced by the same DLL must all be a multiple of 90°.
The 7-bit DQS delay settings from the DLL vary with PVT to implement the phase-shift delay. For example, with a 0° shift, the DQS signal bypasses both the DLL and DQS logic blocks. The Intel® Quartus® Prime software automatically sets the DQ input delay chains, so that the skew between the DQ and DQS pins at the DQ IOE registers is negligible if a 0° shift is implemented. You can feed the DQS delay settings to the DQS logic block and logic array.
The shifted DQS signal goes to the DQS bus to clock the IOE input registers of the DQ pins. The signal can also go into the logic array for resynchronization if you are not using IOE read FIFO for resynchronization.
For Cyclone® V SoC devices, you can feed the hard processor system (HPS) DQS delay settings to the HPS DQS logic block only.
The input reference clock goes into the DLL to a chain of up to eight delay elements. The phase comparator compares the signal coming out of the end of the delay chain block to the input reference clock. The phase comparator then issues the upndn signal to the Gray-code counter. This signal increments or decrements a 7-bit delay setting (DQS delay settings) that increases or decreases the delay through the delay element chain to bring the input reference clock and the signals coming out of the delay element chain in phase.
The DLL can be reset from either the logic array or a user I/O pin. Each time the DLL is reset, you must wait for 2,560 clock cycles for the DLL to lock before you can capture the data properly. The DLL phase comparator requires 2,560 clock cycles to lock and calculate the correct input clock period.
For the frequency range of each DLL frequency mode, refer to the device datasheet.
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