CS 14 -- Train lab

For this lab, we'll be working with a train set that is controlled by some digitial signals. There will be a demo to show you the operation of the trains. The bulk of the project will be done with your entire lab section. As a group, you will design a special-purpose processor to make the control of the trains programmable.

Basic Input/Output for train control

There are both input and output lines that your processor must handle:

Input:
- 1 clock wire, which is yellow, that allow you to share a clock with the rest of the train control.
- 2 photosensor wires, which are connected to the photosensors, one for each track. Note that this line will be asserted when the photosensor is covered, and deasserted otherwise.
Output:
- 4 control wires, over which you will send clocked, 4-bit numbers to provide commands to the train control circuitry. Below is a table of the possible 4-bit numbers and their meaning. Be sure to read the notes that follow the table, as the meaning of each number can change depending on its position in a sequence of numbers.

4-bit train control codes:

Number	Meaning
0	Toggle system on/off
1	Select train 1
2	Select train 2 (Note that there is no train 2)
3	Select train 3
4	Select train 4 (Note that there is no train 4)
5	Reverse selected train
6	Toggle light (Note that to perform this command, you must send this signal, send the train number, and then send the reverse* signal)*
7	Stop the selected train
8 to 13	Set selected train speed to the selected value. (Note that 8 is so slow that you probably shouldn't use it!)
14 to 15	Unused

Notes on train signal use:

As suggested by the semantics attached to the numbers, you must first send a train number on one cycle, and then send a command number on the next cycle.
When the clock edge to the train rises, the train uses whatever code is currently given on the input wires.

Your assignment, loosely stated

You should design a specialized processor that would allow someone to control the train by choosing instructions on your processor. You must select a few instructions that your processor will support, and choose an instruction format---that is, you should choose the instruction word length, as well as the breakdown of bits within the instruction word.

It is important that you design the processor in as modular a fashion as is reasonable. There should likely be some kind of centralized control board that is designed to connect directly to the train control circuitry. Other boards should connect to this controller board, and each be made to handle some subset of your total instruction set.

Information about chips and other parts will be made available as quickly as possible. If there's a part that you think you need, inquire as to whether or not we have it, and consider that you may have to create your own solution from the parts that you've already used.

Scott F. Kaplan

Last modified: Tue Apr 2 09:18:13 EST 2002