Radio Shack TRS-80 Model II Reference Manual page 104

Modell! TRSDOS ....
While spooler is active, and while it is printing out a previously captured file, it
is using the extra processor cycles that would normally be wasted. Previously,
the computer would just wait for certain operations to complete; now, these
small time periods are used by the spooler to get the data from a disk file, then
output them to the real printer. Not only are wait times used, but, just to insure
that your printed report doesn't stop running altogether, some extra' 'time
slices" are given to the spool printer. The spooler, as you can now see, is a true
multi-tasked operation. The technique is more correctly known as
background/foreground processing, where the spool printer is a background
task, and your application program is a foreground task.
The capture function and the printing functions of spooler are separate. It should
be noted that the capture function is directly controlled by the application
program or utility that creates printed data.
In
BASIC, the' 'LPRINT" verb directs
data to the printer. Every time a byte is output to the printer, spooler, when
active, will intercept this byte and either output it to a disk file, as mentioned
above, or to throw it away. The time it takes to write the data out to a disk is
much faster than if it were going out to a real printer, due to the differences in
speed between a disk drive and even the fastest printers that you might use. This
feature alone can be used to speed up long jobs that prepare a printed report as an
output. The trade-off for the increased speed is, of course, disk space. Printed
reports usually take a lot of disk space to store. More on this later.
3. Some of the features that spooler print has that should be helpful are listed
below:
A. The operator has control over the printing of the report from the disk file.
Such controls include pausing the report, stopping it altogether, resuming
the report, restarting the report on a certain line, and starting it up from a
certain line. The line positioning feature is especially useful when you only
need a certain part of a printed report, or if you ran out of paper, or the paper
jammed, while you were printing the report for the I st time.
B. Other operator controls include number of copies, and whether to keep or
delete the spool disk file after printing is complete.
C. Assuming none of the high-RAM where the spooler program resides has been
used for user subroutines, etc. , then the operator has the operational
flexibility to run spooler printing as desired. Again, spooler was designed to
be used without any application program modification to printer functions.
D. Special code has been installed that can sense printer faults in parallel
printers. This causes the printing function to just wait for the problem to get
corrected before the printing will resume. This should be especially helpful
when you have a paper jam or run out of paper. As soon as the printer goes
back on-line and is ready, spooler print will resume. Also, you may stop the
printer by taking it off-line (parallel printer only) so that you may look at the
printed material, and spooler will just "wait" for the printer to go back
on-line. If you have a serial printer that has the ability to send the DC3
character (x' 13 ') and the DC I
(X' I
I') character, then you may use the DC3 to
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