Squeezing FPGA Memory to make an Apple II disk controller #FPGA #VintageComputing
The Big Mess o’ Wires (BMOW) blog discusses developing an Apple II disk controller that’s based on the UDC disk controller.
The original UDC card had 8K of ROM and 2K of RAM, so it needs 10K of combined memory. The FPGA device I’m using for prototyping, a Lattice MachXO2-1200, has 8K of embedded block RAM and 1.25K of distributed RAM. It also has 8K of “user flash memory”.
So will the UDC design fit? It’s close, but I think the answer is no.
I could switch to a larger FPGA with more memory, or add a separate RAM or ROM chip. But that would increase cost and complexity, and anyway wouldn’t help with my prototype board that’s already built.
The post contemplates various ways to squeeze things to fit in the available memory space or consider memory expansion or a larger FPGA.
Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards
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.
Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.
Python for Microcontrollers — Python on Microcontrollers Newsletter: CircuitPython 8.1.0 and 8.2.0-beta0 out and so much more! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi
