'===========================================================================
' Subject: INTERRUPT HELP                    Date: Unknown Date (00:00:00)
' Author:  Earl Montgomery                   Code: QB, PDS                
' Keys:    INTERRUPT,HELP                  Packet: INTERRPT.ABC
'===========================================================================
'$INCLUDE: 'qb.bi'
DIM inregs AS regtypex, outregs AS regtypex
CLS
LOCATE 1, 1: PRINT "For those of you that have mastered the use ";
PRINT "of interrupts, read no further!";
LOCATE 2, 1: PRINT "However if you are like me and still";
PRINT " struggling you might find this interesting.";
LOCATE 3, 1: PRINT "First off whenever you use an interrupt with";
PRINT " QB you need to load QB/L.";
LOCATE 4, 1: PRINT "This loads the QB.QLB library which contains";
PRINT " the code needed to use interrupts.";
LOCATE 5, 1: PRINT "Now you are ready to program! Your first";
PRINT " entry should be '$INCLUDE: 'QB.BI'";
LOCATE 6, 1: PRINT "This file contains the TYPE and Data";
PRINT " structure to be used.";
LOCATE 7, 1: PRINT "List QB.BI from DOS and you will see there ";
PRINT "are two types defined.";
LOCATE 8, 1: PRINT "RegType and RegTypeX. Notice that both are ";
PRINT "identical except that";
LOCATE 9, 1: PRINT "RegTypeX allows the use of the ES and DS ";
PRINT "segment registers.";
LOCATE 10, 1: PRINT "Your next entry should be: DIM inregs as ";
PRINT "regtypex,outregs as regtypex";
LOCATE 11, 1: PRINT "Now we need to call an interrupt. If you ";
PRINT "have the DOS programmers manual";
LOCATE 12, 1: PRINT "look at interrupt &h21 function &h19. This ";
PRINT "interrupt gets the Default";
LOCATE 13, 1: PRINT "Drive and returns the info in AL of register";
PRINT " AX. If AL returns a 0 this";
LOCATE 14, 1: PRINT "represents Drive A. If AL returns a 1 then ";
PRINT "this represents drive B. If AL";
LOCATE 15, 1: PRINT "returns a 2 this represents Drive C and so on."
LOCATE 16, 1: PRINT "Now we need to put something in register AX";
PRINT " and that is the function &H19.";
LOCATE 17, 1: PRINT "INREGS.AX=&H1900"
LOCATE 18, 1: PRINT "Now we call the interrupt."
LOCATE 19, 1: PRINT "CALL INTERRUPTX(&h21,INREGS,OUTREGS)"
LOCATE 23, 28: PRINT "Press any key to continue."
WAIT1:
I$ = INKEY$: IF I$ = "" THEN GOTO WAIT1
CLS
LOCATE 1, 1: PRINT "OK the DOS programmers manual said that the ";
PRINT "info would be returned in AL.";
LOCATE 2, 1: PRINT "How do we read AL from register AX? Use this";
PRINT " formula:";
LOCATE 3, 1: PRINT "AL=AX AND &HFF (More on these formulas later.)"
LOCATE 4, 1: PRINT "PRINT AL"
LOCATE 5, 1: PRINT : PRINT "Let's put everything together and ";
PRINT "see what we have.";
LOCATE 7, 1: PRINT "'$include: 'Qb.BI'"
LOCATE 8, 1: PRINT "DIM inregs AS RegTypeX,outregs AS RegTypeX"
 
 
LOCATE 9, 1: PRINT "inregs.ax=&h1900"
LOCATE 10, 1: PRINT "CALL INTERRUPTX(&h21,INREGS,OUTREGS)"
LOCATE 11, 1: PRINT "AX = (outregs.ax)"
LOCATE 12, 1: PRINT "AL=AX AND &Hff"
LOCATE 13, 1: PRINT "PRINT AL"
LOCATE 14, 1: PRINT "Now let's actually run this program. Ready?";
PRINT " Here goes!";
inregs.AX = &H1900
CALL interruptx(&H21, inregs, outregs)
loop1:
LOCATE 15, 28: PRINT "Press any key to continue."
I$ = INKEY$: IF I$ = "" THEN GOTO loop1
REM Formula to find AL.
AX = (outregs.AX)
AL = AX AND &HFF
REM Looking for a 2 in AL (My default drive is C)
PRINT AL
LOCATE 19, 1: PRINT "Well I got a 2 because my default drive is ";
PRINT "C. How about you?";
LOCATE 23, 28: PRINT "Press any key to continue."
wait2:
I$ = INKEY$: IF I$ = "" THEN GOTO wait2
CLS
LOCATE 1, 28: PRINT "Formulas to read AH and AX."
LOCATE 2, 1: PRINT "Now let's see how we can read AH."
LOCATE 3, 1: PRINT "To find AH the formula is ";
PRINT "AH=(AX AND &HFF00)/256";
LOCATE 4, 1: PRINT "Let's run it and see what we get."
LOCATE 5, 28: PRINT "Press any key to continue."
loop3:
I$ = INKEY$: IF I$ = "" THEN GOTO loop3
AH = (AX AND &HFF00) / 256
PRINT AH
LOCATE 7, 1: PRINT "I got 25. How about you?"
PRINT
LOCATE 10, 1: PRINT "Well we know the value of AL and AH. With ";
PRINT "these two values";
LOCATE 11, 1: PRINT "we can find out what is in AX. The formula ";
PRINT "is AX=(256*ah)+AL";
LOCATE 12, 1: PRINT "In my case AL was 2 and AH was 25. So 256 *";
PRINT " 25 <val in AH> + 2 <val> in AL=6402";
LOCATE 13, 1: PRINT "Let's run it and see what we get."
AX = (256 * AH) + AL
LOCATE 14, 28: PRINT "Press any key to continue."
loop4:
I$ = INKEY$: IF I$ = "" THEN GOTO loop4
PRINT AX
LOCATE 17, 1: PRINT "My values matched how about yours?"
LOCATE 23, 28: PRINT "Press any key to continue."
loop5:
I$ = INKEY$: IF I$ = "" THEN GOTO loop5
CLS
LOCATE 1, 1: PRINT "But someone is saying <But we put &h19> in ";
PRINT "AX how can it contain 6402!";
LOCATE 2, 1: PRINT "Did I mention the AX,BX,CX and DX registers ";
PRINT "are 16 bit registers?";
 
LOCATE 3, 1: PRINT "This means AX is composed of two 8 bit ";
PRINT "registers AL & AH";
LOCATE 4, 1: PRINT "Remember we put &H19 in AH and AL returned a";
PRINT " &h2. Therefore AX contains";
LOCATE 5, 1: PRINT "&H1902. And if you do a PRINT &H1902 you get ";
PRINT "6402. I am printing all";
LOCATE 6, 1: PRINT "values in decimal. Anyway, let's print it now."
LOCATE 8, 28: PRINT "Press any key to continue"
loop6:
I$ = INKEY$: IF I$ = "" THEN GOTO loop6
PRINT &H1902
PRINT "Your value may differ depending on your default drive."
LOCATE 23, 28: PRINT "Press any key to continue."
loop7:
I$ = INKEY$: IF I$ = "" THEN GOTO loop7
CLS
LOCATE 1, 1: PRINT "I hear someone saying <My books show AL on ";
PRINT "the left and AH on the right.>";
LOCATE 2, 1: PRINT "Then why doesn't AX contain &h0219 instead ";
PRINT " of &h1902?";
LOCATE 3, 1: PRINT "My reference books show the same thing and ";
PRINT "that is confusing to me too.";
LOCATE 4, 1: PRINT "But trust me for now AH is on the left and AL";
PRINT " is on the right. Maybe someone";
LOCATE 5, 1: PRINT "can shed some light on why the progrmming ";
PRINT "books show examples with AL on the";
LOCATE 6, 1: PRINT "left and AH on the right."
LOCATE 8, 1: PRINT "How would you like to see how the bit wise ";
PRINT "AND operation with";
LOCATE 9, 1: PRINT "&Hff allows us to read the value in AL? Hey!";
PRINT " Where is everyone going!?";
LOCATE 10, 1: PRINT "Class hasn't been dismissed! Hey come back!";
PRINT " Well for those of you who";
LOCATE 11, 1: PRINT "stayed it is very very simple: The AND &Hff";
PRINT " (255) or binary 11111111 "
LOCATE 12, 1: PRINT "sets all the bits in AH to 0. Therefore all ";
PRINT "we have left is what is in AL."
PRINT "Neat huh?"
LOCATE 14, 1: PRINT "Class is now dismissed."
locate 15,1:print"Your instructor was Earl Montgomery"
LOCATE 23, 28: PRINT "Press any key to continue."
loop8:
I$ = INKEY$: IF I$ = "" THEN GOTO loop8
END