At the download link you can get the firmware 5.06 for VKP80II-SX that groups a dense number of modifications required by you and Andrey during the past months:

- Epson style pagemode
- Added the "Paper Ej-Retracting" setup parameter which enables the "forward-backward" movement for each retract (if safe to do according to the length of printed paper)
- Added the command 0x1C '>' to switch between connected interfaces (COM or USB).
- Added the "Interface" setup parameter to select the default interface to be used at power on.
- Added the "PowerOn Test Jam" setup parameter which produces a small white ticket at power on used to detect paper jam.
- General improvements on paper jam detection.
- Added the "Print" setup parameter to enable or disable the print capability of the printer
- Added the command 0x1C 0xD0 to enable / disable the print capability of the printer.

I would like to release this as official firmware for Ladon's VKP80II-SX.