The number of lines on the printer's physical
display. This value is 0 if there are no lines on the
physical display or if there is no physical display
Additional information:
The printer has two physical lines on the display,
however, in many cases up to four seperate lines
of text may be displayed by alternating pairs of
lines every three seconds. Thus the display really
has four logical lines for displaying messages.
This object will return the number of logical
display lines supported by the printer.