SPO, and its source code SPO.S, constitute a general-purpose
serial-port output-only driver routine for PTDOS.  Characters
are simply transmitted as received.  SPO may be used as the
output file for EDBASIC using SET OF=SPO as a command or SET OF=
"SPO" as a statement, and using standard PRINT statements with
TAB functions, semicolons and whatever in them, which BASIC will
interpret and convert into the appropriate stream of characters.
      SPO may also be used in an EDBASIC program as if it were
a disk file, opened by a "file open" statement such as
FILE #3;"SPO",2,,,256 and then addressed by a "file print"
statement like PRINT #3;A,B$,%13F2,C.  The advantage of the
latter form is that the driver file is opened only once, whereas
using the SET OF syntax results in a disk access to load the
driver each time the SET OF statement is executed.  This may
happen continually, and waste time, if the BASIC program must
frequently shift the output from screen to printer and back.
      Unfortunately, BASIC will not allow semicolons or TABs in
a file print statement.  It substitutes a carriage return (0D)
for each comma as a separator.  This will cause your printer to
return (but not line feed) after each variable and print them
on top of one another if you don't take precautions.  One way
to solve this is to use only one PRINT statement per line of
output, placing the characters to be output into a single long
string appropriately using BASIC's substring functions and FILL
statement.  Assuming the desired print line has been placed in
X$, the statement PRINT #3;X$,CHR(10) will print it and follow
it with a carriage return (due to the comma) and a line feed,
as you would wish.
      An alternative solution is implemented in the SPB driver.
This driver discards the carriage returns that BASIC inserts
between variables; it also treats a backslash "\" as a code
indicating that the next character is a control character, in
the same manner that the BASIC video driver does.  Inclusion of
code for a line feed "\J" in a BASIC print statement will
cause both a carriage return and a line feed to be sent, as they
must be to end any line of printing and move to a new line.  A
carriage return alone, as for underlining, may be specified by
"\M", and any control characters meaningful to the printer or
other device may be specified similarly.  Again, TABs may not
be included in a print statement because BASIC will treat them
as syntax errors, but BASIC's "%" print formatting statements
may be included with the expected effect.  The SPB driver is not
suited for BASIC output using the SET OF syntax, nor for output
of non-BASIC material.
      Reassembly, "scrunching" and typing as a device driver of
the source code of either driver may be accomplished by calling
the MAKDRIVR macro, using the following syntax:
      DO MAKDRIVR,{source filename},{object filename}.