Epson TM-C610 Technical Reference Manual page 84

Printing barcodes and 2D symbols
Sets specified number of point, language of the replaced TrueType font by barcode and 2D
symbol font to the print data.
 The number of point for barcode and 2D symbol is specified; check it from [Barcode
 The original TrueType font can be used only for specifying barcode and 2D symbol;
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and 2D Symbol] on [Driver Utilities]. The barcode and 2D symbol cannot be printed if a
value other than those specified is set.
therefore, if other characters are specified, they cannot be printed. Make sure to use a
TrueType font that will not be used for other printing.