Well, I suppose you have your motor connected to a parallel port of the HC11 (let's say PORTB for this example).
You have to write to the port B with the proper value to control the proper bits in the proper order.
If you use the original configuration of the HC11, the port B is located at address 0x1004.
So, you define a 8 bit pointer variable to point to this address and you change the content of this pointer with the value you need.
function()
{
volatile char *portBPtr = (volatile char *) 0x1004;
...
*portBPtr = 0; /* Clear all bits of port B */
*portBPtr |= 0x4; /* Set bit 2 of PORT B */
*portBPtr |= 0x10; /* Set bit 4 of PORT B */
*portBPtr &= ~0x4; /* Clear bit 2 of PORT B */
*portBPtr &= ~0x10; /* Clear bit 4 of PORT B */
...
}
Hope it helps!