As I understand, the BIOS code/bitstream that held in the ROM should be generic (work alongside with multiple CPU types or ISAs). In addition, I saw mentions in the web that claim to have the possibility to dump it's code (and to 'disassemble' it).
So, in which language, instruction set or machine code is it written? Doesn't it need any kind of processor to perform its operations? If so I guess that it will use the external CPU, then how does it knows the specific instruction set of the employed one?
Maybe it has an internal processor?