DC motor (fig 1) is operated through two terminals, whenever the potential difference is created (through batteries, cells etc) across these terminals the motor starts its motion.
Suppose we have connected a DC motor to our system’s parallel port through a secure circuitry (fig 3).
We wish to operate the DC motor through our parallel port (fig 2) using some input through our keyboard. Like “F” key for running motor in “Forward Direction”, “R” for “Reverse Direction”, “S” for “Stop” and “E” for “Exit from code”.
We have suggested that we will use parallel port’s Pin 2 and Pin 3 (the last 2 pins of parallel port’s data check fig 2 and table 1).
|Pin 2||Pin 3||Outcome|
You have to write a code in assembly language that take an input character from keyboard (S, F, R and E) and on the basis of these characters transmit the code (with respect to the truth table) to the parallel port to operate that connected DC motor.
NOTE: your code only use ASCII code for Capital letters F, R, S and E as an input from the keyboard and will transmit the specific data to the parallel port. Through this program, we are interested in communicating with a DC motor through parallel port.
; show scancode on external LEDs connected through parallel port
oldisr: dd 0 ; space for saving old ISR
; keyboard interrupt service routine
kbisr: push ax
in al, 0x60 ; read char from keyboard port
mov dx, 0x378
out dx, al ; write char to parallel port
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 = 0x012
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