Using I/O Editor

To select the DDR subsystem location, follow these steps:

  1. 1.Click Design Flow > Constraint Manager > I/O Attributes > Edit with I/O Editor.
    Figure 1. I/O Editor
  2. 2.Select the Memory View tab in I/O Editor. Select the appropriate Memory Type to get the valid locations for the memory type.
    Figure 2. I/O Editor—Memory View
    Note: The difference between DDR3 and DDR3L is the I/O standard, SSTL15 and SSTL135 I/O. I/O editor allows to select SSTL15I, SSTL15II, SSTL135I, SSTL135II I/O standards. User needs to select SSTL135 I/Os in the I/O editor for DDR3L configuration.
  3. 3.Select the appropriate DDR instance from the Design View window, and drag it onto Port Function. For the selected DDR instance, the I/O Editor shows the valid locations in green.
    Figure 3. I/O Editor—Valid DDR Locations

In I/O Editor, Design View window, the DDR instances that are assigned and locked are shown in green. I/O Editor does not assign a location if the selected location is unavailable, has insufficient resources or is impacted by any other issue. If an issue is detected, I/O Editor displays an error.

Figure 4. I/O Editor—Assigned DDR Location

To turn ODT on for a DQ and DQS, select the Port View tab, select the signal, and select ON from the On Die Termination list, as shown in the following figure.

Note: 60 Ω ODT is the recommended ODT setting for DDR4 DIMM/on-board DDR4 component. 30 Ω ODT is the recommended ODT setting for on-board DDR3 component. 60 Ω ODT is the recommended ODT setting for DDR3 DIMM.
Figure 5. Setting ODT
Note: If VREF is not specified, the internal VREF is used. When external VREF is used, any I/O pin available on the same bank can be selected as VREF using the I/O Editor. If the DDR Subsystem uses two banks, two external VREF pins are required (one per each bank). Microchip recommends using the internal VREF.

If there is DDR, QDR, and DLL in a design, be aware of the following DLL placement rules: