Rod KM6SN notes that KD8CEC software will run in a stand-alone separate Arduino Nano which is not connected to a uBITX. This means you can look at the CAT serial link operations on your computer.
Rod mounted a spare Nano on perfboard so he could access the UART RX and TX lines and the Nano Reset line, and installed the KD8CEC software on the Arduino Nano. The test jig and ESD ground plate underneath are shown in the photo above.
Some time ago Rod purchased a Saleae 8ch logic analyzer when they were still cheap. I used it, and enjoyed it for about a year. Then, an ESD accident blew the Saleae. I looked online and did not like the new Saleae prices, so I purchased a cheap Saleae clone (USBee AX Pro) for about $12. See:
Unfortunately, the folks at Saleae got upset at all the clones, and changed their software so that it would not work with the clones.
So, I went to the USBee web site to get software, only to find out they wanted $20 for it. Being a true blue amateur op, Rod did not want to pay $20 for proprietary software linked to one piece of hardware only.
After some digging he uncovered what appears to be an excellent open source (i.e. FREE!) logic analyzer called PULSEVIEW/sigrok.
PULSEVIEW provides for decoding protocols, such as I2C, UART, CAN, 1wire, and many more. Sigrok is the command line version, and PULSEVIEW is the GUI on top of the command line that provides a graphical display of decoded serial link. PULSEVIEW/sigrok supports an impressive list of hardware analyzers. Furthermore, PULSEVIEW/Sigrok supports data collection from some digital multi-meters, and digital oscilloscope dongles. For more information see:
Apparently some logic analyzers have an analog channel, and PULSEVIEW can show the analog signal as you would see it on an oscilloscope.
Here is an example PULSEVIEW screen showing a UART serial link decoded.
Channel D0 is Nano UART RX, channel D1 is Nano UART TX, channel D2 is Nano reset line:
Not bad for a $12 investment!!
PULSEVIEW/sigrok installation instructions
For Windows: https://sigrok.org/wiki/Windows#Windows_installers
For Linux: https://sigrok.org/wiki/Linux
After installing Pulseview, install the firmware for the USBee AX using these instructions:
In Linux, use sudo to copy the attached file 99SaleaeLogic.rules into /etc/udev/rules.d
Remember to add your username to the plugdev and dialout groups.