Which is the "write enable" pin of flash memory in Stratix IV GX?
On the Stratix IV GX FPGA Development Kits web page, you'll find the Stratix IV GX FPGA Development Board Reference Manual (PDF) where you'll find the documentation for the MAX II CPLD EPM2210 System Controller beginning on PDF page 15, and the FSM bus flash write enable (FLASH_WEn) in table 2-6 part 3 of 4 on PDF page 18, showing both the MAX II CPLD EPM2210 and EP4SGX230 pin numbers.

In the Stratix IV GX FPGA Development Kit User Guide (PDF) you'll find Appendix A. Programming the Flash Memory Device.