[Donn] wanted know exactly what is going on inside of a processor so naturally he built a CPU out of TTL components. He had previously built a couple of versions of a computer based on the Z80 processor. Using the troubleshooting skills he learned and a second-hand textbook, he set to work using 74LS series chips connected using the wire-wrap method we’re familiar with from other cpu projects.
The finished product runs well at 1.8 megahertz, but he also included a 2 hertz clock and a step clock for debugging. At the slower speeds, the register board (seen at the left in the picture above) lights LEDs and can be used to tell what the CPU is currently working on. Programming is accomplished through either a dumb terminal or a PC running a terminal emulator.
His writeup is from about five years ago but that didn’t prevent us from getting that fuzzy feeling in the geek-center of our brain when we read about it. It is well written and thorough so if you’re into this kind of thing there’s plenty to enjoy.
As promised earlier, the Near Future Laboratory has published an overview of the Logicport Logic Analyzer. They’re using the Playstation 2 analysis as an example. The Logicport uses “interpreters” to define protocols. It has I2C/TWI, SPI, RS232, and CAN 2.0A/2.0B, but you can build your own interpreter based on these. You can specify bit order and the format you want the data in. Slave interpreters can be used for specific tasks: with the PS2 they were used to just show the fifth byte, which is the actual button press.
“Triggers” are used to signal specific activity. On the PS2, one was attached to the falling signal on the slave select line. This event means the master is about to start sending data.
The final area worth exploring is “measurements”. These can be frequency or arbitrary time intervals between events. The Logicport has multiple ground connections to eliminate noise from the signal and you’ll have to play with sample rate and logic level to get things running smooth. It’s nice to see how-tos written from the perspective of someone just getting started with the tool.
SparkFun has always been good about designing and stocking useful breakout boards. This recently added Logic Level Converter is no exception. It’s uses two BSS138 MOSFETs to shift 5V logic levels to 3.3V. The board handles two separate serial pairs. Just hook up the RX and TX on either side. Provide power at both voltages and the board will happily do the conversion. It’s $2, smaller than the size of a quarter, and perfect for plugging into a breadboard.