The Controller - QMS -ps 800+ User Manual

A.1 The Controller
The controller executes
POSTSCRIPT
programs sent to
it from the host computer. During normal operation,
the controller cycles through the following sequence of
steps:
• First, it sets up a clean virtual memory. This
means it prepares a new working environment for
the next job it is about to receive. (Note: Through-
out this manual, the term "job" will refer to a
POSTSCRIPT
program).
• Then it executes the job by interpreting the
POSTSCRIPT
data which it receives from the host
computer as an input file.
• When it encounters an end-of-file indicator (which
marks the end of the job) or an error occurs, the
printer cleans up after the current job and restores
the virtual memory to its initial state in preparation
for the next job.
Ordinarily, each job is executed solely for the purpose of
generating printed pages. However, under certain con-
ditions, a job may change some permanent parameters
in the printer itself, or may perform some computation
whose results are sent back to the host computer.
POSTSCRIPT
data sent to the
QMS-PS
800+ is first scanned
by the
POSTSCRIPT
software which determines the print-
ing/graphic operation to perform. This information is
then processed into a bit-mapped image which is for-
matted and stored into page memory. Printing can now
take place. The printer reads the image information from
page memory, serializes it, and sends it to the print en-
gine via a high-speed video interface.
4-2 Advanced User's Information