Dymo LabelWriter SE300 User Manual page 120

tell it to stop sending data. When there is again room (that is,
space for approximately 30 percent more characters in the
buffer), the printer sends the ASCII code XON (11 hex) to the
computer to tell it to resume sending data. (XON is also known as
DC1; XOFF is synonymous with DC3.) If the computer doesn't
stop sending data after it receives an XOFF, the data that
overflows the buffer will be lost and the printer will halt and its
power LED will flash.
The printer will send an XON code when it goes on-line to get
things started. It will send an XOFF code to stop the computer
from sending information if the input buffer is approximately 50
percent full.
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