Citizen Systems iDP-3550 - Manual (Page 93)

ENQ
[Function] Enquiry
[Code] <05>H
[Outline] This command is valid only for the serial interface. The printer sends the status information.
If this command is entered after receiving the text information in the STX-ETX mode, the
printer will send the status information and check byte.
STX
[Function] Text start
[Code] <02>H
[Outline] This command is valid only for the serial interface. It effectuates the STX-ETX mode.