Standard VGA cards have almost perfect compatibility with EGA, but their compatibility with 6845-based cards is severely limited: MDA and CGA modes are supported only at BIOS level, and there's no compatibility with Hercules Graphics Card (a.k.a. MGA) at all.
Some older VGA cards, however, also have special modes for register-level compatibility with MDA/HGC and CGA.
Cards with compability modes

Chipsets without compability modes

  • Acumos AVGA2/Cirrus Logic CL-GD5402
  • Cirrus Logic CL-GD5422
  • Tseng ET4000

[wiki]Category:ISA cards[/wiki]