Entry-Level Oscilloscopes
It’s time to shop for a new oscilloscope. My trusty HP1631d has served me well, but it’s almost 30 years old, and it’s not even really an oscilloscope but a logic analyzer. This boat anchor is big, heavy, loud, cumbersome,…
Invalid Logic Levels Explained
What happens when you feed an invalid voltage level to the input of a digital logic gate? It’s an interesting story. In my last post, I described a subtle Nibbler bug where a combinatorial feedback loop through the ALU caused…
Sneaky Combinatorial Feedback Bugs
Aha! After four days of tinkering with Nibbler, I finally found the cause of the occasional bad writes to RAM. At first I thought it was a timing problem with the RAM enable signals, then I thought it was bus…
De-Glitching RAM Writes
Yesterday’s Nibbler celebration was premature – I discovered that about one in ten-thousand writes to RAM stores the wrong value. Bad RAM, bad! No biscuit for you! Arghh, what a headache. I first discovered the problem while making improvements to…
Homemade CPU First Boot
YES, IT WORKS! The Nibbler homemade CPU is up and running, and it can play “guess the number” like nobody’s business. Awesome! If you haven’t seen my earlier posts, Nibbler is a 4 bit CPU built from standard 7400 series logic…
Wire Wrapping the Nibbler CPU
Nibbler construction is underway! I’m building the CPU on a 5 x 4 inch perfboard, and connecting the components using wire wrap. This particular perfboard is a Twin Industries 8200 Series, which has continuous metal planes on both sides that…
Son of 3D Graphics Thingy – A Homebrew Graphics Processor
An old project of mine may return from the dead. A few years ago, I started an ambitious project to build a 3D graphics processor using an FPGA. The goal was to create a simple version of the GPU you…
Nibbler Refinements
I’ve made a few refinements to the Nibbler design, and now I’m ready to start building the CPU! After looking at what seemed like a million different possible changes and additions, I’ve decided to keep the hardware exactly as…
Inside Vintage Electronic Toys – How Speak & Spell Works
The 1970s were a great time to be a geeky kid, thanks to the introduction of the first digital electronic toys. With their beeping songs and blinking lights, who could resist them? Recently I decided to take a trip down…
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