Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!hc!lll-winken!scooter!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Determining if a printer is available
Summary: Call BIOS interrupt 17H to find out
Message-ID: <1555@neoucom.UUCP>
Date: 28 Mar 89 20:53:56 GMT
References: <2165@pembina.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 96


Printer operations are handled by the BIOS interrupt 17H.  You
should use the interrupt to access the printer, as there are a
number of packages that daisy-chain into INT 17H for redirecting
output to file file, serial port, etc.  If you play by the book,
you can be a good citizen and work with any TSR programs that might
be hanging around.  Don't bother with the printer table at 0040:08H.
Another reason to use the BIOS is that on AT machines it calls the
BIOS time-out via INT 15 as per "multitasking provisions".

Here is a short example program written in Turbo C.  It should be
relatively portable, as virtually all C compilers have some
function for generating a software interrupt.  Note that when a
printer is plugged in, turned on, and ready to go, you will get a
return code that indicates (Not busy | Selected).  If the printer
is switched off or not attached to the port, you'll get return
values that vary from clone-to-clone, the main thing is that they
will NOT be (Not busy | Selected).

Here is a description of INT 17H summarized from the "IBM Personal
System/2(tm) and Personal Computer BIOS Interface Technical
Reference" pp 2-111 , 2-112:

INT 17H  printer

on entry:
AH=00		print character
AH=01		initialize printer port
AH=02		read status
AH=03 to FF	reserved

AH=00, AL=ascii char, DX=port number 0,1,2
on return:
AH=status
	bit 7=1		not busy
	bit 6=1		acknowledge
	bit 5=1		out of paper
	bit 4=1		selected
	bit 3=1		i/o error
	bit 2,1		(reserved)
	bit 0=1		time-out

AH=01, DX=port number 0,1,2
on return:
AH=status
	same as above

AH=02, DX=port number 0,1,2
on return:
AH=status
	same as above

---------------------------- cut here -------------------------
#include <stdio.h>
#include <dos.h>

void main()
{
        struct REGPACK preg;
        int mask=1;

        printf("Enter number of LPT port for status check: ");
        scanf("%d",&preg.r_dx);

        preg.r_dx = --preg.r_dx & 0xff;
        preg.r_ax=0x0200;
        intr(0x17,&preg);

        printf("\nPort returns the following status:\n");
        while (mask<256) {
                switch(preg.r_ax>>8 & mask) {
                        case 0x80:
                                printf("\tNot busy\n");
                                break;
                        case 0x40:
                                printf("\tAcknowledge\n");
                                break;
                        case 0x20:
                                printf("\tOut of paper\n");
                                break;
                        case 0x10:
                                printf("\tSelected\n");
                                break;
                        case 0x08:
                                printf("\tI/O Error\n");
                                break;
                        case 0x01:
                                printf("\tTime-out\n");
                        }
                mask*=2;
                }
} /* end of main */

----------------------------------------------------------------
Bill
wtm@impulse.UUCP or wtm@neoucom.UUCP