LVDS SERDES IP, Agilex 3, Quartus 26.3

We have encountered a potential regression in the LVDS SERDES IP between Quartus Prime Pro 26.1 and 26.3 when targeting the Agilex 3 (A3CZ025BB18A).

Environment:

• Quartus Prime Pro 26.1 – LVDS SERDES IP version 24.1.0
• Quartus Prime Pro 26.3 – LVDS SERDES IP version 25.0.0
• Device: A3CZ025BB18A
• Interface: LVDS SERDES, RX, 8:1, source-synchronous external clock
• I/O standard: TDS_1P3

Problem description:

The exact same project compiles successfully with Quartus 26.1 but fails during Fitter in Quartus 26.3.

The error reports a termination conflict between the physical I/O pin and the LVDS SERDES byte:

• Physical pin assignment: DIFF_TERMINATION = DIFF
• I/O buffer termination: TERMINATION_RT_DIFF
• SERDES byte parameter: PINxxxx_DIFF_TERMINATION_RT_OFF

I verified that all differential input pins have the correct DIFF_TERMINATION assignment in the QSF.

HDL generation difference:

In LVDS SERDES IP version 24.1.0 (Quartus 26.1), the generated HDL assigns:

TERMINATION_RT_QPDS_UNSET

to the RX byte differential termination parameter.

In LVDS SERDES IP version 25.0.0 (Quartus 26.3), the generated HDL explicitly assigns:

TERMINATION_RT_OFF

for RX pins.

Changing this assignment back to TERMINATION_RT_QPDS_UNSET in the generated HDL allows Quartus 26.3 to complete the Fitter successfully.

Questions:

1. Was the change from TERMINATION_RT_QPDS_UNSET to TERMINATION_RT_OFF intentional in LVDS SERDES IP version 25.0.0?
2. Is this a known issue or regression affecting Agilex 3 true differential inputs using TDS_1P3?
3. What is the correct recommended configuration to use the internal 100-ohm differential termination with the LVDS SERDES RX interface?
4. Is there a newer IP version, patch, or recommended workaround that avoids modifying generated HDL files?
5. Does using TERMINATION_RT_QPDS_UNSET preserve the intended internal 100-ohm differential termination when DIFF_TERMINATION = DIFF is assigned in the QSF?

We would appreciate clarification on whether this is an IP generation issue or a Fitter issue in Quartus 26.3.

Best regards