accessing card memory from grub

[Raz]

Hello

I have a device that has a dip switch. This dip switch controlls
the way the computer boots ( Intel processor );
I need to read the dip switch setting from grub.
I assume that grub use physical memory mappings and not virtual addressing is done.
So, Question:
Given the fact that I know what is this memory location , how can i access it from grub ?

thank you