HalfBurntToast's Stuff

Overview TFORTH is my custom version of FORTH. It started as a programming exercise that grew into a somewhat usable language. This version of FORTH is a bit odd in that it has no compiling mode at all . Not even bytecode compiling. Everything is 100% interpreted. So, it's essentially a fancy text parser. It also doesn't try to be ANSI compliant at all. That being said, it does support a lot of common FORTH things like you would expect, including: custom function definitions, calling external functions via function pointers, full access to the system's memory map, input/output, etc.   Variables There are some big differences, under-the-hood, with this version of FORTH. For one, there are no variables. Instead, I define variables as functions with a index to the "variable page," a page in memory dedicated to temporary storage. So, for example,    5 0 ! would assign the literal value 5 to index 0 in the variable page. So, to declare a "variable," I would d...

One feature/limitation of my computer design is that it uses an Arduino to replace a lot of extra logic and interface components. Specifically, the Arduino performs the following functions: Serial I/O The computer piggy-backs off of the Arduino's built-in serial to USB interface chips to communicate with the host laptop. Power-up reset circuitry The 6502 needs to run for 50 or so full clock cycles with the RESET line held low, and then RESET is sent high for normal operation. System clock Because the computer uses the Arduino's USB interface, the Arduino must be kept synchronous to the computer. If the computer runs too quickly, it could outpace the Arduino's ability to read and send data.   The last point is the most important of all. The Arduino must be kept in lock-step with the computer at any given time in order to ensure that I/O data isn't missed. Thus, the the clock output is just a digital output from the Arduino. This means that the computer's maximum spee...

Version 1.0 Even though the protoboard computer works, and I successfully worked with it for months, it has some significant drawbacks: Difficult to modify Making any changes to the system requires maneuvering through a trunk of wires with an iron. Fragile Multiple wires are often joined to a single pad. This requires the solder joint to be reheated/reflowed multiple times. A wire that pops loose would be difficult to reattach. Not worth reproducing It took about three days of soldering to get the computer connected. Repeating that task is not something I was looking forward to. The obvious solution is to make a PCB version of the board. It always seemed kind of silly to me to make a PCB version of a one-off project. But, it's either that or doing it all by hand again. So, after following along with the excellent KiCAD tutorials by Shawn Hymel, I set out to put the computer onto copper.  A tricky thing about computers of this era is managing the bus lines between devices. The most...

Since I was a teenager, something I've always wanted to do was design and build a computer, chip-by-chip. I was inspired by the movie Pirates of Silicon Valley, specifically when Steve Wozniak built a computer, the Apple 1, that started an empire. So, I started learning electronics with the main goal of making my own computer.   Breadboard Shenanigans   In 2018, I finally got around to working with the legendary 6502 CPU and built my first rudimentary computer that barely worked. This version of the computer relied on an Arduino Mega to act as an EEPROM and serial interface. Thus, the entire computer needed to be synchronized to the Arduino to function. Unfortunately, building computers on breadboards is a pretty frustrating task. Breadboards are prone to manufacturing defects that can cause intermittent shorts between components, intermittent connections between the breadboard and components, massive amounts of parasitic capacitance and inductance. All of which are incre...

It's literally been ten years since I've updated this blog. Honestly, I forgot it existed. Since then, I've gone through three college degrees, three jobs, and more projects than I can even remember. I've worked in IT (security, networking, server admin, etc), programming, hardware diagnostics and development. Everything from managing servers, to programming hardware drivers, to developing circuits. I can say now that I've even been paid to design PCBs professionally for specialty analog sensors. But, thanks to 2020, I've had more time on my hands to meddle in the tech world on my own. Over just this past year, I've designed multiple homebrew computers from breadboarding to PCB fabrication. I've written, mostly in assembly langauge, everything from hardware drivers, to a scripting language, to simple games for these computers. I've hacked the driver board for a standard digital typewriter and turned it into a teletype. I reverse engineered a TTY tele...