What's taking so damn long? That's a good question. Turns out modeling a video state counter in Verilog is much harder than I'd thought. I'm probably making it harder than it needs to be. But when you don't have a timing chart to compare against, and are just working with the description in the Clocks… Continue reading Status Report
0111 – Missing Parts
As I slowly near completion of my timing circuit board, I've been adding components to their sockets and testing the different signals they produce. The basic signals (14MHz, 7MHz, 3.5MHz, etc.) seem to be clocking correctly. Having the quartz oscillator socketed allows me to remove it and replace it with a simple 1kHz 555 timer-based… Continue reading 0111 – Missing Parts
0110 – Timing is everything
Before I get much further with the video module, I need to properly flesh out the heartbeat of the system: the timing circuit. As mentioned previously, the /// uses a 14.318MHz clock. The reason for such a high frequency is that (apart from other components in the system) the video module needs synchronized clocks at… Continue reading 0110 – Timing is everything
0101 – Video output
Now that I've completed a basic 6502-based computer, my next milestone is to implement a video output system. The Apple ///'s video system was unique, in that it provided similar video modes to the Apple II, as well as additional modes to display higher resolutions with many more colors. Additionally, unlike the II which was… Continue reading 0101 – Video output
0100 -Milestone 1: a running program
Today marks the completion of my first milestone: running a program in ROM and keyboard input/ display output through the ACIA to USB-serial bridge. A happy day to say the very least. Another "Hello World" of a fully-functioning computer. Once wire wrap was completed (and failed, then troubleshot, rewrapped, repeat...), I began the task of… Continue reading 0100 -Milestone 1: a running program
0011 – RAM and I/O
Getting to the free-run stage is easy. Where it gets complicated is when you add hardware to make your fancy program counter into a real computer. When you're doing a project like this, its assumed you are willing to put in the time to learn some electronics in order to move forward. Both the journey… Continue reading 0011 – RAM and I/O
0010 – Free Run and Hex Display
The first test of every new microprocessor "single-board" project is free-run. Once the CPU, clock, and reset circuitry is in place, we hardwire the data bus to supply the data pins on the 6502 with its opcode NOP (No-Operation). The hexadecimal for the NOP instruction is $EA. This is a simple do-nothing opcode that basically… Continue reading 0010 – Free Run and Hex Display
