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.
CHUMP Task Sequence
You are about to embark on a hardware project that holds the promise of being one of the most important achievements of your young scholastic career, that is, to build a 4-bit computer from scratch. Reaching the summit will test your passion, dedication, and commitment to an engineering undergraduate program. D. Raymond and J. Corley accomplished the feat in their 2018/2019 ICS4U year:
- 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 DER entry in your CHUMP Report. Your goal will be to demonstrate that the program you write this week, will run on the processor you build six weeks from now.
- 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 you MUST use the following parts I supply you with: Quad breadboard, 500 kΩ trim pot, rectangular LEDs (red, green, yellow), 3×555 timers, strip of 0.1μF caps, TTL AND, OR, NOT logic ICs, slide switch, and 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.
- Program EEPROM. As a replacement for the complex combinational logic circuitry that would provide dynamic control for our processor's various modules and to provide storage for the machine language version of our program, we need to construct an EEPROM programmer for the two AT28C16 parallel EEPROM ICs our build requires. The Arduino nano or UNO serves as control for our programmer. Task. After viewing Eater's two (incredible) videos, create the programmer sketch and flash your code from Stage 1 into the AT28C16 EEPROM you have been provided with.
Thinking ahead...as each of you will be required to create a shield for the Dolgin Development Board, an implementation of this programmer (that uses a 24Pin ZIF socket) based on the ATtiny84 would be a wonderful legacy asset for the DES.
- Program Counter. After stripping everything from your CHUMP platform with the exception of your FULL Eater-style clock circuit, add the ICs you were supplied with in class in a layout similar to the graphic to the right. There is no need to wire them ALL this week, In this segment, you are expected to limit your wiring to your clock, the SN74LS161 counter and your AT28C16 Program EEPROM that you flashed last weekend. Eight rectangular LEDs on the output pins of the Program EEPROM will confirm your program is loaded and ready for execution in the next phase. So, IN THIS ORDER,
- Strip off ALL your previous builds, with the exception of the full Eater Clock build. Confirm this clock is still fully functional with an LED indicator. Do not proceed until this is working. Ok, good.
- Now, wire in the SN74LS161 counter ONLY, reading the strikingly simple notes on the IC provided on page 36 of the Feinberg handout you were provided with. Place 4 tightly-arranged, east to red, rectangular LEDs (no resistors required) on the outputs of the SN74LS161 to confirm the counting, just as you did EXACTLY in Grade 10 with the 4510. Do not proceed until this is working. Ok, good.
- Now, wire your four SN74LS161 outputs to the A0-A3 address inputs of your Program EEPROM. I think you can figure out what to do with the three control pins (/WE. /OE, and /CE). Place the rectangular LEDs you were given on the 8 I/O outputs of the EEPROM to confirm you're seeing the program that you successfully flashed last weekend. DONE.
- For this segment's accompaying video, you are asked to lead off with exactly three full executions of your CHUMP code, at 1 Hz, so viewers (me) can witness the precise LED representation of your machine language instructions. On the heels of that you can engage in a discussion of your build.
- Write the Report and submit.
- IC (Optional). This stage requires that you introduce your peers to the specific CHUMP IC that you have been assigned (above) in the form of a clear and detailed 5-minute in class presentation. After which, over the course of the next few weeks, as questions arise from your classmates about your IC you will be required to provide answers and possible solutions. A fourth entry in your DER's CHUMP Report will summarize your presentation.
- Control EEPROM. Your second AT28C16 EEPROM with the Control codes indicated in the table (below, right) flashed onto it, has been returned to you. Insert the IC into your platform. After our group review of the bits in each code, strategically reposition the IC, if necessary.
- Processor. Ok, here we go...After serious planning and layout considerations, using the TTL chipset described above, lengths of colour-coordinated hookup wire and rectangular LEDs available to you to, position all your processor's ICs and wire up the rest of your CHUMP.
- 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):