Example 9.7 ; display a tick count on the top right of screen [org 0x0100] jmp s
ID: 3616440 • Letter: E
Question
Example 9.7
; display a tick count on the top right of screen
[org 0x0100]
jmp start
tickcount: dw 0
; subroutine to print a number at top left of screen
; takes the number to be printed as its parameter
printnum: push bp
mov bp, sp
push es
push ax
push bx
push cx
push dx
push di
mov ax, 0xb800
mov es, ax ; point es to video base
mov ax, [bp+4] ; load number in ax
mov bx, 10 ; use base 10 for division
mov cx, 0 ; initialize count of digits
nextdigit: mov dx, 0 ; zero upper half of dividend
div bx ; divide by 10
add dl, 0x30 ; convert digit into ascii value
push dx ; save ascii value on stack
inc cx ; increment count of values
cmp ax, 0 ; is the quotient zero
jnz nextdigit ; if no divide it again
mov di, 140 ; point di to 70th column
nextpos: pop dx ; remove a digit from the stack
mov dh, 0x07 ; use normal attribute
mov [es:di], dx ; print char on screen
add di, 2 ; move to next screen location
loop nextpos ; repeat for all digits on stack
pop di
pop dx
pop cx
pop bx
pop ax
pop es
pop bp
ret 2
; timer interrupt service routine
timer: push ax
inc word [cs:tickcount]; increment tick count
push word [cs:tickcount]
call printnum ; print tick count
mov al, 0x20
out 0x20, al ; end of interrupt
pop ax
Example 9.7
; display a tick count on the top right of screen
[org 0x0100]
jmp start
tickcount: dw 0
; subroutine to print a number at top left of screen
; takes the number to be printed as its parameter
printnum: push bp
mov bp, sp
push es
push ax
push bx
push cx
push dx
push di
mov ax, 0xb800
mov es, ax ; point es to video base
mov ax, [bp+4] ; load number in ax
mov bx, 10 ; use base 10 for division
mov cx, 0 ; initialize count of digits
nextdigit: mov dx, 0 ; zero upper half of dividend
div bx ; divide by 10
add dl, 0x30 ; convert digit into ascii value
push dx ; save ascii value on stack
inc cx ; increment count of values
cmp ax, 0 ; is the quotient zero
jnz nextdigit ; if no divide it again
mov di, 140 ; point di to 70th column
nextpos: pop dx ; remove a digit from the stack
mov dh, 0x07 ; use normal attribute
mov [es:di], dx ; print char on screen
add di, 2 ; move to next screen location
loop nextpos ; repeat for all digits on stack
pop di
pop dx
pop cx
pop bx
pop ax
pop es
pop bp
ret 2
; timer interrupt service routine
timer: push ax
inc word [cs:tickcount]; increment tick count
push word [cs:tickcount]
call printnum ; print tick count
mov al, 0x20
out 0x20, al ; end of interrupt
pop ax
Explanation / Answer
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