I'm looking for tools to help me analyze the communication between the main board and control panel of a Canon Pixma MX340 multi-function inkjet. The data is asynchronous serial 250000-8-E-1 so Wireshark was the wrong tool for the job. Wireshark can perform much of the data manipulation tasks I wished for, but it works for network packets and not general serial data.

Focusing my search on serial data tools for an electronics hobbyist, I came across several mentions of something called Bus Pirate. This is something I had been aware of. In fact, I bought one several years ago upon recommendation by another hobbyist, but I have yet to put it to work for any of my own projects.

The core usage scenario for a Bus Pirate is programmatic access to some basic common electronic interfaces like SPI, I2C, and my current focus: asynchronous serial. The idea is that we can experiment with these interfaces using interactive commands, versus writing a microcontroller program that we have to compile and upload to flash on every change. That's gives us an immediate turnaround time versus 20-30 seconds, time that will really add up when performing rapid iteration. For example, in the tentative early stages of bootstrapping a new piece of hardware.

In addition to the data interfaces, Bus Pirate also provide control over some interface-adjacent tools. The one that caught my eye is the ability to provide 5V and 3.3V DC power, and to turn them on/off on command. Again, this is very useful in early stages of working with new hardware, because if we mess up commands and accidentally put the hardware in a bad state, we can quickly turn it off and back on again with a command instead of unplugging anything and plugging it back in.

In hindsight, a Bus Pirate would have been really useful when I was experimenting with salvaged I2C LCD screens, allowing faster experimentation. At the time, I had forgotten I had a Bus Pirate gathering dust on the shelf. I don't think a Bus Pirate would have been useful for a car audio face plate, though. Due to the fact they used Sanyo's CCB protocol and that's not something Bus Pirate understands.

I think Bus Pirate will be useful soon, because after I take this MX340 completely apart I want to try repurposing the control panel. I should be able to impersonate the main board by using my own hardware to play back the command sequences I've captured and analyzed. Getting that up and running should be a perfect opportunity to finally use my Bus Pirate for its designed purpose.

But a Bus Pirate won't be helpful for me right now, because I want to listen in on existing communication and not interfere. Which means I want two UART receive wires, and the Bus Pirate only has a single UART with a single transmit wire and a single receive wire. The type of data filtering I want to perform isn't part of core Bus Pirate functionality, either. As Bus Pirate itself has long been discontinued, I quickly skimmed over the spec sheet for its successors GoodFET (also discontinued) and GreatFET One (currently active product), but they don't seem to have added the kind of features I want right now. My search continues.

This teardown ran far longer than I originally thought it would. Click here to rewind back to where this adventure started.