🚀 go-pugleaf

I have come across what appears to be a confusing discrepancy.
In Terry Dettmann's book "Dos Programmer's Reference", Que Corp.,
1988; (an excellent book in my opinion),

on page 425 it states that:
      BIOS Interrupt 0Bh is used by COM1 & COM3 on the PC & XT,
      & is used by                  COM2 & COM4 on the AT.


      Similarly on page 426 it states that:
      BIOS Interrupt 0Ch is used by COM2 & COM4 on the PC & XT,
      & is used by                  COM1 & COM3 on the AT.

I have a terminal emulation program that is hard-coded for COM1,
but uses Interrupt 0Ch.  This program works on both PC and AT
class machines!

Also I believe that most PC/XT bioses do not support COMs 3 & 4.

Since I am trying to write a terminal emulation program, I need to have
this discrepancy sorted out.  Can anybody enlighten me?

-- 
	 L.Piacenza - Chemistry Department - University of Transkei
	 Internet: sppp@hippo.ru.ac.za  Tel. 27-471-3022384
	 Internet: chpp@unitrix.utr.ac.za