Defining a Homemade CPU’s Instruction Set Architecture, Decoder, & RAM
If you happen to be designing your own CPU, you might be interested to study the work done by those before you. In this post by Colin “Domipheus” Riley topics such as ISA, Decoders, and RAM and tackled; this is part 3 in an ongoing blog series that is now nearly 1 year old.
This is a 16 bit machine, and I want to keep things simple. To that end, we use a fixed instruction length. Each instruction will always be 16 bits long, regardless of what it does. This allows our instruction decoder to be much simpler. However, fitting all the information we need into an instruction may be difficult. In the last part, I mentioned we have a register set comprising of 8 16-bit registers, meaning we need 3 bits to address one. I’ve not decided to have any of the registers special, like r0 always being zero. All are addressable.
8-6-2021 (August 6, 2021) is the Snakiest day of the year and it’s also this year’s CircuitPython Day! The day highlights all things CircuitPython and Python on Hardware. See you there!
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.