For my B-day this year, my dear wife offered me two great gifts (or toys as she likes to call them). Today, I will review the Heathkit/Zenith ETW-3400, a CPU trainer kit launched in 1976. This specific model was sold in 78 and is in fantastic shape even 37 years later. This kit is similar to others that you may have crossed – especially in Europe during the 80’s – such as the Micro-Professor MPF-x (and its arguable Apple ][ compatibility). The idea behind the ET-3400 is fairly simple and efficient.
If you want to learn microprocessors and digital electronics – even hands-on if you went for the kit versus the pre-assembled models – then these trainers were a great solution. It is not a surprise that the ET-3400 was very popular, even with Universities. You may not know this, but there was a time when using a microprocessor was not obvious and applications were still to be discovered! Today, all these “chips” are so ubiquitous that we don’t think about them anymore. My point being is that especially because of this ubiquity, these kits still have a tremendous educational potential today. Indeed, once you’ve started playing around with an Arduino, Pie or Galileo, sure you can build stuff, but you will likely not learn the next level down and understand how software interacts with hardware. And this is the layer where you can learn the most – sure, it is harder, but you will definitively sharpen your skills! The ET-3400 is pretty simple and is truly a very basic computer: it has a CPU (Motorola 6800 @ 1MHz), RAM (256 Bytes) and a monitor in 1 KB ROM. And here you go.
To be complete, the kit has few extra goodies that really makes your life easy (in addition of the monitor – for the younger readers, a monitor is a program that allows you to mess with your system’s CPU’s registers & memory, and even debug your code step-by-step), like a keyboard, six LED segmented display as well as a prototyping section to expand your system. I do not have one, but an extra expansion unit was also available to add IOs for example – which is pretty useful if you do not want to re-enter your program each time you power the trainer up. Note that the power switch doesn’t work as you would expect – fortunately – since the unit is in fact always on. Similarly, the reset does not clear the content of your RAM (that’s really cool). One other cool advantage vs. my Altair 8800 for example, is the auto input mode. Instead of using the pretty laborious deposit/examine sequence when entering your machine language codes, you just specify the starting address, and each byte code entered is stored, and the write address is incremented for you (and you are keying-in hex values instead of switching-in binary codes). Overall, this kit is really cool! A really nice B-day gift indeed.