There are plenty of well-known models among the 8-bit machines of the 1980s, and most readers could rattle them off without a thought. They were merely the stars among a plethora of others, and even for a seasoned follower of the retrocomputing world, there are fresh models from foreign markets that continue to surprise and delight. [Dave Collins] is treating us to an in-depth look at the VTech VZ-200, a budget machine that did particularly well in Asian markets. On the way, we learn a lot about a very cleverly designed machine.
The meat of the design centres not around the Z80 microprocessor or the 6847 video chip, but the three 74LS chips handling both address decoding and timing for video RAM access. That they managed this with only three devices is the exceptionally clever part. While there are some compromises similar to other minimalist machines in what memory ranges can be addressed, they are not sufficient to derail the experience.
Perhaps the most ingenuity comes in using not just the logic functions of the chips, but their timings. The designers of this circuit really knew the devices and used them to their full potential. Here in 2025, this is something novice designers using FPGAs have to learn; back then, it was learned the hard way on the breadboard.
All in all, it’s a fascinating read from a digital logic perspective as much as a retrocomputing one. If you want more, it seems this isn’t the only hacker-friendly VTech machine.
John Dalton, CC BY-SA 3.0.
