Nintendo header

About 33% of licensed Nintendo NES games have an header present at their last bank, at addresses $ffe0-$fff9, right before the interrupt vectors.

The info in them is frequently incomplete and/or inaccurate. When info on a particular filed is not present, a byte $00 or $ff is used for padding

• $ffe0-$ffef : Name of the game, in ASCII, zero terminated (sometimes the name is abbreviated or replaced by Nintendo's code). ASCII codes 20h-5Ah allowed. Supposed to be right-justified.
• $fff0-$fff1 : PRG checksum (either the last 16k bank, or the whole PRG-ROM). Clamped sum of all bytes, excluding the two checksum bytes.
• $fff2-$fff3 : CHR checksum. 0x00 if RAM
• $fff4 : Data sizes. Values: 0 = 8KB,1 = 16KB,2 = 32KB,3 = 128KB,4 = 256KB,5 = 512KB (No provisions for 64KB, 0 is usually used)
  • D7-D4: PRG size
  • D3: 0 = CHR ROM, 1 = CHR RAM
  • D2-D0: CHR size
• $fff5 : Board Type.
  • D7: 0 = H Scroll, 1 = V Scroll (invert to interpret as mirroring)
  • D6-D0: 0 = NROM, 1 = CNROM, 2 = UNROM, 3 = GNROM, 4 = MMC (any)
• $fff6 : Version ($01 by default, incrementing on revisions)
• $fff7 : Valid Title Length - 1. 0 if no title entered.
• $fff8 : Maker's code, the same used for the FDS, GB, GBC and SNES headers : 1 = Nintendo, 2-254 = everyone else. 255 must be reserved.
• $fff9 : Header Validation Byte. 8-bit checksum of FFF2-FFF9h should = 0