watcom inline assembly got error "Illegal use of register"

Question

I use the Open Watcom IDE V1.9, and Target Environment is DOS-16bit,image type is exe. target cpu is 80386.

Here is my source code:

#include <stdio.h>

void getITV(int n);
unsigned int ITV[16];

void main()
{
    int i=0;
    for(i=0;i<16;i++){
        getITV(i);
        printf("%x   ",ITV[i]);
    }
    printf("\n");
}

void getITV(int n)
{
    int*  address ;
    n = n * 2;
    address     = (int*) ( (int)ITV + n );
    __asm{
        push es
        push ax
        push bx
        mov ax,0
        mov es,ax
        mov ax,n
        mov bx,es:[ax]            --<this line is the one create error>--
        mov word ptr [address],bx
        pop bx
        pop ax
        pop es
    }
}

when i make it, I got this:

cd D:\watcom-project\dumpIVT
wmake -f D:\watcom-project\dumpIVT\dumpIVT.mk -h -e -a D:\watcom-project\dumpIVT\getCS.obj
wcc getCS.c -i="C:\WATCOM/h" -w4 -e25 -zq -od -d2 -3 -bt=dos -fo=.obj -mm
getCS.c(28): Error! E1156: Assembler error: 'Illegal use of register'
Error(E42): Last command making (D:\watcom-project\dumpIVT\getCS.obj) returned a bad status
Error(E02): Make execution terminated
Execution complete

Well, but I cannt see how Line28 is wrong, I checked the open watcom user guide, but in section "In-line Assembly Language", there are no information about Why I got this error. Any suggestion?

Answer 1

You can't use ax register of 80x86 processor in 16-bit mode to access memory locations, or at least not in this way. Try to use one of the index register instead, like si or di, for that