PHY Lite for Parallel Interfaces Intel® FPGA IP User Guide

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ID 683716
Date 12/13/2021
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2.4.1. Input Buffer Reference Voltage (VREF)

The POD I/O standard allows configurable VREF. VREF range selection via QSF for POD 1.2 V requires the following .qsf assignments:

set_instance_assignment -name VREF_MODE DDR4_CAL -to <pin_names>
set_instance_assignment -name VREF_MODE DDR4_CAL_RANGE2 -to <pin_names>

The VREF settings are at the lane level, so all pins using a lane must have the same VREF settings including general-purpose I/Os (GPIO).

Table 19.  VREF_MODE Description
VREF Mode Description
EXTERNAL Use the external VREF. This is the default.
DDR4_CAL Use internal VREF generated using code set via dynamic reconfiguration. VREF range is 60%–92.5%.
DDR4_CAL_RANGE2 Use internal VREF generated using code set via dynamic reconfiguration. VREF range is 45%–77.5%.
Note: You must select the VREF range for your design using analog simulation.
Figure 19. VREF


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