AES and MVS BIOSes compute their own checksums and compare them against the 16bit value at address $000080. The checksum is a simple byte sum of the whole ROM except locations $000080 and $000081.
AES (all versions ?)
Screen color meanings (information by Channelmaniac):
- Blue: All tests passed (The AES does not test the Z80 sound IC).
- Red: Work RAM error ($100000 region).
- Green: Palette RAM error ($400000 region).
- Yellow: Video RAM error (programmed through custom port).
- Pink: BIOS checksum error (0xC00000 region).
- Cyan: Memory card error (only tested if card in unit and blank).
MVS (SP-E VERSION 0)
Information by Channelmaniac:
When a MVS board is powered up without a cartridge installed, the border color around the edges of the crosshatch screen indicates the BIOS region:
- Green: 6 slot, an older BIOS
- Light blue: USA BIOS, labelled SPU2
- Dark blue: Spanish BIOS, labelled SPS2
- Red: Japanese BIOS, labelled SPJ2
Check order ?
- WORK RAM ERROR (68k RAM)
- BACKUP RAM ERROR (Battery-backed RAM)
- COLOR RAM BANK0 ERROR (First bank of 256 palettes)
- COLOR RAM BANK1 ERROR (Second bank of 256 palettes)
- VIDEO RAM ERROR (VRAM)
- CALENDAR ERROR
- SYSTEM ROM ERROR (BIOS ROM checksum fail)
- MEMORY CARD ERROR
- Z80 ERROR (no reply to sound command $01)