When using Quartus® Prime software versions 15.1.2 and earlier, Arria® 10 devices do not support the Slow slew rate setting for the SSTL-135, SSTL-125, SSTL-12 and POD12 I/O standards. The slew rate setting defaults to the Fast setting, as Slow slew rate is not compatible with on-chip output termination.
Programmable current strength settings with Fast and Slow slew rate support (where applicable) is enabled for SSTL-135 Class I/Class II, SSTL-125 Class I/Class II, SSTL-12 Class I/Class II and POD12 I/O standards in Quartus Prime software version 16.0.