Assembly Language for Intel- Assembly Language for Intel- Based Computers Based Computers Chapter 16: Expert MS-DOS Programming (c) Pearson Education, 2006-2007. All rights reserved. You may modify and copy this slide show for your personal use, or for use in the classroom, as long as this copyright statement, the author's name, and the title are not changed.
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Assembly Language for Intel-Based Assembly Language for Intel-Based ComputersComputers
Chapter 16: Expert MS-DOS Programming
(c) Pearson Education, 2006-2007. All rights reserved. You may modify and copy this slide show for your personal use, or for use in the classroom, as long as this copyright statement, the author's name, and the title are not changed.
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 2Web site Examples
Expert MS-DOS ProgrammingExpert MS-DOS Programming
• Interrupt Handling • Terminate and stay Resident Programs
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 3Web site Examples
Interrupt Handling Interrupt Handling
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 4Web site Examples
Interrupt Vectoring ProcessInterrupt Vectoring Process
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 5Web site Examples
OverviewOverview
• Interrupt handler (interrrupt service routine) – performs common I/O tasks• can be called as functions
• can be activated by hardware events
• Examples:• keyboard handler
• divide by zero handler
• Ctrl-Break handler
• serial port I/O
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 6Web site Examples
Interrupt Handling Interrupt Handling
Executing Interrupt Handlers:-
• software interrupt • Hardware Interrupt
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 7Web site Examples
Interrupt Handling Interrupt Handling
Interrupt Control Instructions:-
• STI instruction (enable external interrupts)
• CLI instruction (disable external interrupts)
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 8Web site Examples
Writing a Custom Interrupt Handler
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 9Web site Examples
Ctrl-Break Handler Example
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 10Web site Examples
Ctrl-Break Handler Example
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 11Web site Examples
Ctrl-Break Handler Example
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 12Web site Examples
Terminate and Stay Resident ProgramsTerminate and Stay Resident Programs
• (TSR): Installed in memory, stays there until removed• by a removal program, or by rebooting
Mov ah,31h
Mov dx, code_Length
Int 21h
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 13Web site Examples
Interrupt Vector TableInterrupt Vector Table
• Each entry contains a 32-bit segment/offset address that points to an interrupt service routine
• Offset = interruptNumber * 4
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 14Web site Examples
TSR Example: printing a character when print TSR Example: printing a character when print screen button is pressedscreen button is pressed
.Model tiny
.code
Jmp init
Start_TSR:
push ax
push es
mov ax,0b800h
mov es,ax
mov es:[0],’A’
mov es:[1],07
pop es
pop ax
iret
Init:
mov ax,0
mov ds,ax
Cli
Mov word ptr ds:[20],offset start_TSR
Mov word ptr ds:[22],CS
sti
Mov dx, offset init
Mov ah,31h
Int 21h
End
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 15Web site Examples
TSR Example: make the print screen button TSR Example: make the print screen button acts as the Caps Lock acts as the Caps Lock
.Model tiny
.code
Jmp init
Start:
push ax
push es
mov ax, 40h
mov es, ax
xor byte ptr es : [17h], 01000000b
pop es
pop ax
iret
Init:
mov ax, 0
mov ds, ax
Cli
Mov word ptr ds:[20],offset start
Mov word ptr ds:[22],CS
sti
Mov dx, offset init
Mov ah,31h
Int 21h
End
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 16Web site Examples
TSRTSR
1 1 1 1 1 1 1 1
7 6 5 4 3 2 1 0 (bit position)
Insert mode onCaps lock is onNum lock is onScroll lock is onALT key held downCTRL key held downLeft shift key held downRight shift key held down
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 17Web site Examples
TSR Example: toggles the Caps Lock every TSR Example: toggles the Caps Lock every 55ms 55ms
.Model tiny
.code
Jmp init
Start:
push ax
push es
mov ax, 40h
mov es, ax
xor word ptr es : [17h], 01000000b
pop es
pop ax
iret
Init:
mov ax, 0
mov ds, ax
Cli
Mov word ptr ds:[1ch*4],offset start
Mov word ptr ds:[1ch*4+2],CS
sti
Mov dx, offset init
Mov ah,31h
Int 21h
End
Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 18Web site Examples
TSR Example: toggles the Caps Lock 3 times TSR Example: toggles the Caps Lock 3 times
.Model tiny
.codeJmp initCount db 0Start:
push axpush escmp cs:[offset count], 3je Fininc cs:[offset count]mov ax, 40hmov es, ax xor word ptr es : [17h], 01000000b
Fin:pop espop axiret
Init:
mov ax, 0
mov ds, axCli
Mov word ptr ds:[1ch*4],offset start
Mov word ptr ds:[1ch*4+2],CS
sti
Mov dx, offset init
Mov ah,31h
Int 21h
End
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