System self-test
AES and MVS system ROMs compute their own checksums and compare them against the 16bit value at address $000080. The checksum is a simple byte sum of the whole system ROM except locations $000080 and $000081.
Checks order ?
Cartridge systems
Information by Channelmaniac.
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| MVS | Crosshatch | WORK RAM ERROR | COLOR RAM BANK0/1 ERROR | VIDEO RAM ERROR (VRAM) | SYSTEM ROM ERROR | MEMORY CARD ERROR |
| Meaning | All tests passed (AES does not test the Z80). Cartridge not detected or not present. | Work RAM error ($100000 region) | Palette RAM error ($400000 region) | Video RAM error | System ROM checksum mismatch (0xC00000 region) | Memory card error (only tested if card present and blank) |
The UniBios case
The Universe BIOS does not use the above color codes to indicate errors.
MVS checks
Additionnal checks are performed on MVS systems:
- Backup RAM: BACKUP RAM ERROR (Battery-backed RAM)
- RTC chip: CALENDAR ERROR
- Z80: Z80 ERROR
When a MVS board is powered up without a cartridge inserted, the border color around the edges of the crosshatch screen indicates the system ROM region:
- Green: 6 slot (ROM name ?)
- Cyan: USA, SPU2
- Blue: Spanish, SPS2
- Red: Japanese, SPJ2