I ordered an MCU programmed with the 3.0.2 firmware to update the Geoff Graham version of the VT100 terminal that I built some years ago. I replaced the 8 MHz crystal with a 20 MHz part and plugged in the new MCU. The unit was inoperative. I queried the seller about this, but did not receive any usable help. He kept referring me to a Hackaday article describing some sort of hardware hack, which didn’t shed any light on the problem. Clear documentation on what needed to be done to adapt the VT100 unit to the new MCU should have been included with the product.
I do not appreciate being brushed off by a seller with advice to refer to something somewhere on the Internet, especially when that something is a long-winded article that is of no interest to me. If what I needed to know to get my VT100 unit working was in there, it was likely in a fragment of a schematic that I don't recognize from the documentation I originally got from Mr. Graham’s website (also, I'm color-blind and can’t read schematics drawn with certain color combinations). I did search the seller’s Github depository looking for a schematic that I could compare to the original Graham design. I was hoping to find a PDF with the required information, but all I could find was something in Kicad format, for which I have no software.
Bottom line is I was sold a useless part.