Star TSP800 Série Mode D'emploi page 19

(2) Hexadecimal Dump Mode
Open the printer cover, then turn the power on while holding the FEED button.
When the cover is closed, "*** HEX DUMP PRINTING ***" is printed, and
the printer enters the Hexadecimal Dump Mode.
Each of the signals sent from the computer to the printer will be printed out
in hexadecimal code.
This function allows you to check if a control code sent to the printer by the
program being used is correct or not. The final line is not printed if its data is
less than one full line. However, if the FEED button is pushed, the final line
is printed. To turn off the mode, it is necessary to turn off the printer
completely.
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