FRGD_MIX
WriteReg16(FRGD_MIX, FSS_BITBLT | 0x07); // 7 = GXcopy rop
WriteReg16(FRGD_MIX, FSS_FRGDCOL | 0x07); // 7 = GXcopy rop
WriteReg16(FRGD_MIX, FSS_FRGDCOL | 0x07); // 7 = GXcopy rop
WriteReg16(FRGD_MIX, FSS_FRGDCOL | 0x00); // 0 = GXinvert rop