This document is derived from information composed by William Levak
(wlevak@sdf.org), mostly from the "Pet Personal Computer Guide".
According to him, the control codes seem to be fairly consistent
with the IEEE printers, but the serial printers seem to be quite
different.  The secondary address are consistent with all Commodore
printers.

Printer Control Codes
CHR$(1)                Enhance on (rest of line).
CHR$(17)   CRSR DWN    lower case (rest of line)
CHR$(18)   RVS         Reverse on. (rest of line)
CHR$(19)   HOME        Top of form if paging enabled.
CHR$(129)              Enhance off.
CHR$(145)  CRSR UP     upper case.
CHR$(146)  RVS OFF     Reverse off.
CHR$(147)  CLR         Enable paging.

Secondary Addresses
 0  Print data exactly as received.
 1  Print data using format.
 2  Set format for printing.
 3  Set lines/page.
 4  Enable diagnostic messages.
 5  Define character 254.
 6  Set line spacing. (not all printers)
 7  Set text mode characters. (not all printers)
 8  Set graphics mode characters. (not all printers)
 9  Disable diagnostic messages. (not all printers)
10  Reset printer. (not all printers)
11  Set unidirectional printing. (8023P only)
12  Set bidirectional printing. (8023P only)
13  Set 15 cpi. (8023P only)
14  Set 10 cpi. (8023P only)
15  Enable correspondence (overstrike) mode. (8023P only)
16  Disable correspondence (overstrike) mode. (8023P only)
17  Print bit image graphics. (8023P only)
18  Print received bit image graphics again. (8023P only)