'This is the strangest program I've ever written, but it is the most dramatic
 'demonstration of interrupt handling I can put into 50-75 lines of code. This
 'program intercepts the clock-tick "user" interrupt 1C, which is invoked 18
 'times per second.  Every time it is invoked, we paint the entire screen blue
 'with white text.  Then we SHELL to DOS.  The neat thing about our INT1C
 'routine is that it keeps executing even when we are in a DOS shell, thus
 'allowing us to run any text-based program (like PB or dBASE or PDS, etc) in
 'this color. Some of you will be inspired by the implications of this, others
 'will not get the point. Making things turn blue is not the ends. This just
 'shows you what incredibly neat things you can do with PowerBASIC. -Erik
 '==============================[PUT THIS NEAR BEGINNING OF PROGRAM]========
 $LIB ALL OFF
 $ERROR ALL OFF
 $STRING 1'.............use these metastatements to shrink memory requirement
 $COM 0
 SG??=CODESEG(INT1C)  '.......................INT5 is a label in this program
 PR??=CODEPTR(INT1C)
 GetInterruptVector &H1C,SG1C??,PR1C?? '.........Get the OLD handler pointers
 '..............................Point the new INT1C vector to our asm routine
 SetInterruptVector &H1C,SG??,PR??
 SHELL '...................Now shell to DOS, while our handler remains active
 SetInterruptVector &H1C,SG1C??,PR1C?? 'restore old vectors (you MUST do this
 SetInterruptVector &H23,SG23??,PR23?? 'before you exit the program or POOF!)
 PRINT "Later on, Man"
 END
 ' **************************************************************************
 'This intercepts INT1C, turns everything blue, and then IRETs
 INT1C:
 !       PUSH    AX              ; Save the whales
 !       PUSH    BX
 !       PUSH    CX
 !       PUSH    DX
 !       PUSH    SI
 !       PUSH    DI
 !       PUSH    BP
 !       PUSH    DS
 !       PUSH    ES
 !       MOV     AX,&HB800       ; Color video RAM segment
 !       PUSH    AX              ; push video RAM segment
 !       POP     ES              ; Pop it into ES
 !       MOV     AL,&H17         ; Color (1=blue, 7=white) attribute
 !       MOV     BX,1            ; first offset attribute in vid ram
 !       PUSH    BX              ; push it
 !       POP     DI              ; and pop it out into DI
 !       MOV     CX,2000         ; number of attributes in video RAM
 Loop1:
 !       MOV     ES:[DI],AL      ; Put the addribute into video RAM
 !       INC     DI              ; increment our pointer to text byte
 !       INC     DI              ; increment again to next attribute byte
 !       LOOP    LOOP1           ; loop number of times in CX

 !       POP     ES              ; Restore my heart
 !       POP     DS
 !       POP     BP
 !       POP     DI
 !       POP     SI
 !       POP     DX
 !       POP     CX
 !       POP     BX
 !       POP     AX
 !       IRET                    ; Interrupt RETurn
 ' **************************************************************************

 SUB SetInterruptVector(Intr%,Segment??,Offset??)
 REG 1,&H2500 + Intr%
 REG 4,Offset??
 REG 8,Segment??
 CALL INTERRUPT &H21
 END SUB

 SUB GetInterruptVector(Intr%,S??,O??)
 REG 1,&H3500 + Intr%
 CALL INTERRUPT &H21
 S??=REG(9)
 O??=REG(2)
 END SUB