Given that ACES is an acronym for Advanced Computer Engineering School it seems reasonable to introduce students to just that: building their own processor from scratch. As Ken Shirriff reminds us, "Before the microprocessor era, minicomputers built their processors from boards of individual chips." It is highly instructive for ACES to physically manipulate and explore this precise architecture prior to their undergrad years, so here we go...
Of the variety of designs to choose from, our preference is for a 4-bit design based on TTL chips due to their availability, project documentation, and suitability for our background. PDF Reference: A Simple and Affordable TTL Processor for the Classroom. D. Feinberg.
- Code. With reference to the CHUMP Instruction Set, develop and submit a unique and (somewhat) interesting CHUMP program (presented in the manner below) as your first ER submission of your ICS4U year. Take advantage of the fact that you are free to add one additional instruction (logic, arithmetic or conditional in nature). Your goal six weeks from now will be to demonstrate that the program you write today will run on the processor you build.
- 5V Clock. Following Ben Eater's terrific 4-part video series on the 555-based Clock module, build, test and report on your own module. This will be the heartbeat of your CHUMP. For this project use MUST the following parts I supply you: breadboard, 1MΩ trim pot, DPDT PB switch (soldered to socket), rectangular LEDs (red, green, amber), 3×555 timers, strip of 0.1μF caps, TTL AND, OR, NOT logic ICs, bags of 0.3" and 0.4" preformed jumper wires. Please take great care with these parts; they are not replaceable. Power can come from a 5V AC/DC adapter or your Arduino for the time being. Finally, for both your text and video presentations, strive to be as clear, concise, and detailed as Eater has been in his presentation, even going one better than him with a video that is under 3 minutes.
- Arithmetic and Logic Unit (ALU). Assemble, test, and report on the SN74LS181 ALU Module. This stage represents the final independent exploratory module before we attempt to build our entire processor. Using the components you have been provided with (additional breadboard, 3" coloured jumper wires, SN74LS181, bargraph and 270 Ω bussed resistor network) and employing ACTIVE HIGH logic, wire up an ALU circuit that can be used to explore the 32 functions (16 logic and 16 arithmetic) the IC is capable of performing. For this submission only, arrange your circuit so that it closely matches the diagram below. (SN74LS181N.fzz) Note. If you're using Fritzing for your processor the generic IC component is probably your best bet. The inspector allow you to edit some characteristics. Finally, make a sincere effort to lay our your board with care and consideration so that your ALU video is clear, informative, and compelling to view.
- Processor (Common). Ok, the big, next-to-last, module. After serious planning and layout considerations, using the TTL chipset described above, lengths of colour-coordinated hookup wire and LEDs available to you to, position all your processor's ICs on your chosen breadboard platform. The TTL ICs are NOT replaceable, so use the IC pullers provided to GENTLY relocate ICs, if necessary. For the purposes of confirming the Program Counter and Program EEPROM are functioning correctly, I have preflashed your Program EEPROM with the contents depicted in the screen capture below, right (click to enlarge). Two 3" jumper wires, on the input addresses A4 and A5, can be repositioned to address each of the four output test sequences. Complete the wiring up to the point where the four output test sequences can be confirmed.
Once this is completed, return your Program EEPROM to me and I will flash the sample (common) code from Step 1 above onto it. The supplied Control EEPROM already has control codes flashed onto it. Complete the wiring of the full processor, perform testing and complete the ER reporting for this module.
- Completed Processor. For this final stage I would suggest confirming Feinberg's Sample Code (below, left) with the Control EEPROM contents (below, right). Once this appears to be functioning you finally consider the code you submitted in the initial phase, hopefully making a MINIMUM of adjustments to it, knowing now what you did not appreciate then. Once you've settled on the program, you are to provide me with a hexadecimal encoding of both your program and its corresponding control codes. I will use this information to flash your EEPROM and return it to you for final testing and execution of your processor. Add one final subsection to your CHUMP project in your ER and complete the final Media and Reflection sections.
- Presentation Day. Congratulations! You have completed a task unlike any other you or anyone else has ever undertaken. On this day you have the opportunity to demonstrate to your peers that you have developed a one-of-a-kind processor capable of running software in a language that you, yourself, designed and implemented. Simply amazing :)
Jackson Russett's EEPROM Programmer Shield (Rollover):