HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

EN Primary and Secondary Fonts 8-5
At a minimum, only the characteristics of the new font that differ from
those of the previously designated font must be sent (the short font
selection method). However, HP recommends that all of the
characteristics be sent to ensure that the correct font is
selected.
Note PCL 5 printers can print any number of distinct fonts per page, limited
only by available memory.
Primary and Secondary Fonts
The printer maintains two independent font select tables for use
in selecting a primary font and a secondary font. All of the
characteristics previously described apply to both tables. This
provides access to two distinct fonts, only one of which is selected
at a given time. To alternate between the primary and the secondary
font, the control codes ‘‘SI’’ (Shift In; ASCII 15) is used to designate
primary and ‘‘SO’’ (Shift Out; ASCII 14) is used to designate
secondary.
The factory default state is primary font designated.
Font Resolution
With the introduction of the LaserJet 4 printer, fonts can be printed
at 600 dpi resolution. All scalable fonts automatically print at either
300 or 600 dpi resolution. A bitmapped font which was designed at
300 dots-per-inch can be printed on the LaserJet 4 printer at 600 dpi.
However, a bitmapped font which was designed at 600 dpi is not
available for selection at 300 dpi resolution.