An unexpected cold shower made it clear that I need a new controller for our solar warm water heating system ("split architecture" which is typical for installation in middle and northern Europe - thanks @Saabman for helping me understand that I had...
Having found the send speed setting, I got a bit interested in the file sending process itself. Tracing back a reference to "Sending....Press any key to stop. " text, I find sub_F013:F013 ; XXX prepare to send (flags and prompt) F013 sub_F013:...