cs401 Computer Architecture and Assembly Language Assignment No. 03 June 2012

[Vuhelper]

; show scancode on external LEDs connected through parallel port

Code:

[org 0x0100] jmp start oldisr: dd 0 ; space for saving old ISR ; keyboard interrupt service routine kbisr: push ax push dx in al, 0×60 ; read char from keyboard port mov dx, 0×378 out dx, al ; write char to parallel port pop ax pop dx jmp far [cs:oldisr] ; call original ISR start: xor ax, ax mov es, ax ; point es to IVT base mov ax, [es:9*4] mov [oldisr], ax ; save offset of old routine mov ax, [es:9*4+2] mov [oldisr+2], ax ; save segment of old routine cli ; disable interrupts mov word [es:9*4], kbisr ; store offset at n*4 mov [es:9*4+2], cs ; store segment at n*4+2 sti ; enable interrupts mov dx, start ; end of resident portion add dx, 15 ; round up to next para and keyboard comprisan code for this problems are e = 0×012 r= 0×13 f= 0×21 s=0x1f