This lab will add 32K of external memory, and two additional parallel I/O ports, to your board. The 32K memory will be located at addresses from $2000 to $9FFF. When operating in the expanded mode, the 68HC11 uses Ports B and C to provide addresses and data for external devices. In order to compensate for losing these two valuable ports, we will also add a Motorola 68B21 Peripheral Interface Adapter to provide two I/O ports similar to Port C of the 68HC11. These two ports and their control registers will be located at memory addresses $B000 to $B003.

The attached schematic shows the necessary wiring to complete the memory expansion. Also attached is a wiring list which tells you exactly which pins to wire together, and a layout diagram showing how to lay out the parts on your board.. The parts and tools needed to do the wiring will be distributed in lab this week. The wiring should be complete and ready to check during your laboratory of Wednesday March 18 or Thursday March 19.

A few notes about the wiring:

• Position and solder all components before doing any wiring. After some wiring is done, it will be impossible to solder something to your board without burning the insulation off some of your wires.
• Solder all pins which need electrical contact to the board. Solder two opposing pins of components where electrical contact is not needed, but physical stability is.
• To wrap a wire onto a pin, strip about 3/4" to 1" of insulation from one end of the wire. Wrap that end of the wire onto the pin, making sure a small amount (about 1/2 turn) of insulated wire is wrapped around the pin. Cut the wire to the necessary length to reach the next pin, strip insulation from the free end, and wrap that end.
• Use different colors of wires for different functions. E.g., use blue wires for address lines, yellow for data, white for control, red for power and green for ground.
• Start with one group of pins (e.g., address), and do all wiring for that group before moving on to the next group. I did the wiring in this order:
  1. Power and Ground
  2. Control Lines
  3. AD0-7
  4. A0-7
  5. A8-15
  6. PIA Ports A and B
• Wire long wires first, short wires last.
• Route wires around the outside of the sockets.
• Do not daisy-chain power and ground lines from one component to another. Instead, fan out from a power or ground pin to the components.
• Take a highlighter pin and highlight the wires you have run on your wiring list as you wire them.
• After all the wiring is done, take an ohmmeter and check the continuity of all wires on the wiring list. (Check continuity after you've run the first few wires just to make sure your wiring technique is correct.)