IDEAL
MODEL small
STACK 100h

DATASEG
    var1 dw 5
    var2 dw 6
    var1Param equ [bp + 6]
    var2Param equ [bp + 4]

CODESEG
proc exchange near
    push bp
    mov bp, sp
    mov ax, [var2]
    mov bx, [var1]
    mov var1Param, ax
    mov var2Param, bx
    pop bp
    ret 4
endp

start:
    push [var1]
    push [var2]
    call exchange
exit:
    mov ax, 4c00h
    int 21h
END start