24
Mar

UM232H = $20 Logic Analyzer

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Long story short, the UM232H can easily be turned into a 7.5 Msps Logic Analyzer (async 245 mode) with some added software (in progress).

What is a Logic Analyzer? No, it doesn't explode when an anti-vaxer blows into it. Nor does it help explain why the opposite sex is clearly crazier than you. A logic analyzer simply allows you to capture, display and decode digital signals. Very helpful when debugging your robot army, or making little Arduino circuits work.

Some friends and I wanted to build a really fast FPGA based Logic Analyzer (LA), but we all have lives (unfortunately?) and many other side projects. During the early design phase, we selected the FTDI FT232H USB IC as the link to a computer. After reading through the datasheet a bit, I noticed that it may be possible to have that single IC function as a low speed logic analyzer. Even better, FTDI sells a small $25 dev board for the FT232H called the UM232H that plugs directly into a breadboard and saves us work (other dev boards 1, 2). When it became clear that the group didn't have the time required to bring an epic FPGA design to life, we decided to try wrangling the UM232H into a cheap LA. The idea was to have the UM232H sample its 8 input pins as fast as possible and dump the data upstream to a computer for analysis and storage. This idea isn't novel as there are many other cheap analyzers (read: Saleae clones) that do that exact thing with a Cypress FX2 IC. However, the FTDI IC is 2-3 times cheaper than the more capable Cypress IC, and I was looking to learn something new anyway.

The diagram below shows the wiring required to make the UM232H work as a cheap LA.

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