Help needed with enabling A20-line

[Jerkko]

I now trying to write a code to enable the A20-line but i have problems with it. I have read someone other's code but there is two things that I don't understand.

Example code is from http://www.osdever.net/tutorials/a20.php?the_id=4

Code: Select all

;; Tell the controller we want to read the current status.
;; Send the command D0h: read output port.
mov AL, 0D0h
out 64h, AL

Where that D0h comes from. Does that tell something for controller like "check incoming things" or something like that?

In that example code is often tested if the controller is ready for a command. Why is that?

[AR]

Something to remember about A20 is that it's a very old legacy, there are more than 30 ways to enable A20, learning how they work is pointless because once it's done you won't need the knowledge beyond that point, A20 is about the only thing I would recommend just copy and pasting.

Anyway, according to the comment, 0xD0 is the "request read port" command.