CITIZEN CT-S310II - Manual (Page 33)

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While paper is loaded, press and hold the FEED button while turning the power
on. Hold the FEED button down for about one second and then release it to start
self-printing. The printer prints its model name, version, memory switch
settings, and a list of built-in fonts.
4.4 Self-printing
Buffer size
Serial communication
status
Interface
Firmware version
Memory
switch
setting