Thank you for that but as I said before this board is 32 bit and I am having to use Atom and PlatformIO to do any work on the ChiTu STM32 chip. I did install STM32Flash on the Pi so that Octopi is ready to try a firmware transfer, but since I can't yet connect and I have no file to upload anyway I shall have to wait for that. I am having to learn as I go. Marlin 2.0 for this board is nearly there but if one looks on YouTube, for eaxample, one finds that there are virtually no uploads concerning STM32F103 boards. I suppose everyone is in the same boat as me, waiting for Marlin and playing with the ChiTu boards. There are a few guys working on other makes of printer with 32bit chips and that helps me a lot.
I have found a file of the factory X5SA-400 firmware and will try to backup my X5ST-400 before I start but want to get the second board first. Better safe than sorry.
Finally received the new board which will connect and stay connected with Octoprint 1.4.0. However it seems that the board was delivered with the firmware for an X5SA-400 and not an X5ST-400 and so although it will load a print and raise the temperatures it will not move in the Z-axis. I cannot find the firmware for the ST and there seems to be no way to get Marlin into the machine as yet so I am still stuck.
Have you made any progress with this? here a couple links that might help. https://www.tronxyonline.com/Firmware-X5SA-400-Series-a63179.html
http://www.customize-3d.com/chitu-g-code-explained.html
Thank you for that but no, I have still not managed to print anything after nine months. The best firmware I found had everything working but the Z-stops did not work and the printhead just crashed into the bed.
I now have six different files for the X5SA-400 and three for the ST. None are correct and all are different, giving different failures.
I have downloaded from the page you specify and will try the firmware this morning.
Thanks again.
Martin.