Подскажите где можно достать описание портов...

Вот что говорит об этом Ralf Brown's Interrupt List (part D):

----------P00EB------------------------------
PORT 00EB - Intel "Triton" chipset - ???
SeeAlso: PORT 0085h"Triton"

00EB ?W ???
----------P00EB------------------------------
PORT 00EB - DUMMY PORT FOR DELAY???
Note: on a number of machines, the BIOS appears to write a copy of any
data sent to numerous other ports to this port as well; it seems
to be a dummy port used for short delays between writes to other
ports (used instead of JMP $+2, which no longer delays on Pentium+)
SeeAlso: PORT 00ED"DUMMY"

00EB ?W ???

Похоже на правду. Спасибо.