The ATSAMV71Q21 has on-die series termination on every I/O pin as shown in Figure 1.
Some of the pins that belong to the External Bus Interface (EBI) are connected to the on-board SDRAM and the Xplained Pro LCD connector (EXT4). When a cable is plugged into the LCD connector long stubs are created on the signal lines, the stubs create ringing that reduces the maximum clock speed, which can be used when communicating with the SDRAM.
For more detailed information about termination strategies, see application note AT91-AN02: Signal Integrity and AT91 Products.
All designs should be simulated using an IBIS file for the ATSAMV71Q21 and the target peripherals to check that the signals are within the limits of the devices.
