Altera DDR SDRAM High-Performance Controllers and ALTMEMPHY IP - Manual (Page 42)

3–16 Chapter 3: Parameter Settings
DDR or DDR2 SDRAM Controller with ALTMEMPHY Parameter Settings
External Memory Interface Handbook Volume 3 June 2011 Altera Corporation
Section I. DDR and DDR2 SDRAM Controllers with ALTMEMPHY IP User Guide