HP 4 FAMILY - Manual (Page 126)

Negative Motion
Command
The Negative Motion command specifies whether negative
motion will be used, thus determining whether the full page
must be buffered before printing can begin.
?&a#N
# = 0 - Picture contains negative motion (page
formatting printers)
1 - Picture contains no negative motion (swath
printers)
Default = 0
Range = 0, 1
If the page contains no negative motion, using the ?&a1N
command increases print speed.
Negative motion includes:
Vertical motion toward the top of the page
HP-GL/2 operations
Print directions other than 0 degrees
Landscape text
When the top of the character cell on the next line is
above the top of the character cell on the current line
The default value of 0 delays printing until all the
processing of input data for a page is complete. This is for
software that needs to compose the data before printing.
A value of 1 allows data to be printed as received, rather
than first stored in a buffer. Otherwise, printing will be
delayed until all processing of input data is complete.
Note This command must be sent before any printable data is
received by the printer.
2-90 Printer-Specific Differences