Oki LD670 User Manual page 169

1.HEX DUMP mode
Then, press and hold down the FEED switch for one second or longer to accept
the selection.
When "HEX DUMP" is printed, press and hold down the FEED switch for one
second or longer to place the printer in hex dump mode.
In hex dump mode, all signals sent from the host computer to the printer are
printed as hexadecimal codes. The printed data can be used to confirm that
the correct control codes have been sent to the printer by a created program.
To reset this mode, turn off the power switch once.
Sample hex dump test printout
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