🚀 go-pugleaf

In article <1992Jul22.114740.2882@hippo.ru.ac.za>, sppp@hippo.ru.ac.za (Prof P Piacenza) writes:
>
>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


COM1 is usually 0x3F8, and IRQ 4, which is interrupt 12, or 0x0C
COM2            0x2F8,     IRQ 3                     11,    0x0B
COM3            0x3E8      IRQ 4                     12,    0x0C
COM4            0x2E8      IRQ 3                     11,    0x0B


I have heard/read somewhere that for PS/2, COM3-COM8 all share a common
interrupt line (either IRQ 3 or IRQ 4, I don't recall which) COM1 & COM2,
though, are pretty standard.


   Scott C. Sadow
   scott@mycro.UUCP
   ...gatech!nanovx!mycro!scott