Device Family: Arria® II GX, Arria® GX, Stratix® II, Stratix® II GX, Stratix® III, Stratix® IV E, Stratix® IV GT, Stratix® IV GX

Type: Answers

Area: EMIF, Intellectual Property


IP Product: DDR SDRAM Controller supporting ALTMEMPHY

Why is CAS latency of 2 or 2.5 not supported for DDR SDRAM Altmemphy or DDR SDRAM High Performance Controller?

Description

The reason CAS latency of less than 3 are not supported for DDR SDRAM Altmemphy and DDR SDRAM High Performance Controller is due to the postamble logic path having a minimum enable latency from address output to dqs enable time. On Stratix® II, Stratix III, Stratix IV along with Arria® GX and Arria II GX devices this latency is too long and hence requires CAS latency of greater than 2 or 2.5 to work reliably. There is no fix/workaround to implement CAS latency of 2 or 2.5.

You will have to set CAS latency of 3 even for lower speeds.