mov ah,01h int16h, how to use it to change the direction of the snake

Question

.model small
.data
var db  '@', '$'

delaytime db 10
total db 0
col db 40
row db 12
.stack 100h
.code
delay proc
    mov ah, 00
    int 1Ah
    mov bx, dx

jmp_delay:
    int 1Ah
    sub dx, bx
    cmp dl, delaytime
    jl jmp_delay
    ret

delay endp

lefty proc
dec col
cmp col, 0
jle sn

leftyie:
mov dl , col
mov dh , row
xor bh, bh
mov ah, 02h
int 10h
ret 

sn:
mov col, 79
jmp leftyie
lefty endp



righty proc
inc col
cmp col,79
jg zero

rightyie:
mov dl,col
mov dh,row
xor bh, bh
mov ah, 02h
int 10h
ret 

zero: 
mov col,0
jmp rightyie
righty endp



upy proc
dec row
cmp row, 0
jl upzero

uptie:
mov dl,col
mov dh,row
xor bh, bh
mov ah, 02h
ret

upzero:
mov row,24
jmp uptie

upy endp


downy proc
inc row
cmp row, 24
jg gozero

downty: 
mov dl,col
mov dh,row
xor bh, bh
 mov ah, 02h
int 10h
ret 

gozero:
mov row,0
jmp downty
downy endp

video proc
mov al, 03h ;set video mode
  mov ah, 00h
  int 10h
  ret
 video endp

start proc
     ;starting coordinates
   mov dh, 12 ;row
   mov dl, 40 ;column
   xor bh, bh
   mov ah, 02h
   int 10h 
   ret
start endp

dashclear proc
mov ax, 0600h
mov bh, 07h
xor cx, cx
mov dx, 184fh
int 10h
ret
dashclear endp

getchar proc
mov ah, 00h
int 16h
ret
getchar endp


main  proc
mov ax, @data
mov ds, ax


 call video
 call start
   mov dx, offset var
   mov ah, 09h
       int 21h


 mov cx, 3200h  ;stop cursor blinking
 mov ah, 01h
 int 10h

call start
getinput:

call getchar ;get character


direct_change:
cmp ah, 72
je w 
cmp ah, 80
je s 
cmp ah, 75
je a 
cmp ah, 77
je d

cmp al, 119
je w 
cmp al, 115
je s 
cmp al, 97
je a 
cmp al, 100
je d

cmp al, 119
jne rak 
cmp al, 115
jne rak
cmp al, 97
jne rak 
cmp al, 100
jne rak


a:
call delay
call dashclear
call lefty
mov dx, offset var
mov ah, 09h
int 21h



jmp a


s:
call delay
call dashclear
call downy
mov dx, offset var
mov ah, 09h
int 21h

jmp s


d:
call delay
call dashclear

call righty
mov dx, offset var
mov ah, 09h
int 21h

jmp d


w:
call delay
call dashclear

call upy
int 10h
mov dx, offset var
mov ah, 09h
int 21h

jmp w

rak:
jmp getinput

main endp
end main

i have this code that moves a single character using w,a,s,d how do i use mov ah,01h int16h so that i can move the character while the character moves on its own if i dont press any key to change its direction.

i was thinking that there should be a timer where when the timer ends amd the user did not press anything the character should keep on going to the direction where the last key was pressed then if the user pressed any the control buttons it should change direction

Documentation of asm code is crucial. Add some comments along the opcodes! — Seki

mcleod_ideafix mcleod_ideafix · Accepted Answer · 2015-04-03T05:01:40

i was thinking that there should be a timer where when the timer ends amd the user did not press anything the character should keep on going to the direction where the last key was pressed then if the user pressed any the control buttons it should change direction

That's is precisely the way to go. Your character would update its position, for example, on every tick of the system timer. If programming for real mode MS DOS on a PC compatible (or emulator), as I assume you are doing, you can just wait until there is an interrupt using the HLT instruction. Don't issue any CLI instruction however, or your program will stuck forever in the HLT instruction.

Do forever
  HLT  ;waits until an interrupt triggers. Usually, every 55ms on IBM PC
  if key pressed
    update direction
  EndIf
  Update character
EndDo

mov ah,01h int16h, how to use it to change the direction of the snake

1 Answers