OSDev.org

Hello,

Keyboard controller has a command to perform power-on reset function. ( 0xFF ) When you issue this command, keyboard controller hard-resets and sets default values.

Until a few days earlier, all was working perfectly. I tried my os on my old 486 machine and realized when I issue this keyboard command, A20 line is reset back to "disabled"; no suprise leading to crash. My other AMDXP 1700+ has no problem, A20 remains set. I guess, because A20 is routed through port 0x92.

Can anyone verify or dis-verify this? is internal power on reset command 0xFF for keyboard controller supposed to reset A20 line? or is it just my old 486?

Thanks in advance.

i use this command, and it doesn't disable A20 for me. Linux uses it in its KB handler (or used to) and it didnt reenable either, so i assume its not meant to touch A20.

i couldnt find a datasheet that said it either did or didnt disable A20 however, so i may be wrong