Something

unsigned short *textmemptr;

unsigned char *memset(unsigned char *dest, unsigned char val, int count)
{
    while (count--) 
    {
        *dest++ = val;
    }
    return dest;
}

int main()
{
    textmemptr = (unsigned short *)0xB8000;
    memset((unsigned char *)textmemptr, '\0', 80 * 80 * sizeof (*textmemptr));
    asm("cli; hlt;");

    return 0;
}