User`s manual

7–15Digital Emulation
Special Parsing Requirements
Parsing is the process of separating a programming statement into basic units
that can be translated into machine instructions. Special parsing requirements
are necessary when invalid parameters are specified, when invalid control
functions are specified, and when control characters are embedded in control
functions. Generally, the printer recovers from these conditions by
performing as much of the function as possible (or, parsing the valid
parameter from the invalid).
When control sequences are not recognized by the printer or when selective
parameters are invalid, the printer ignores them. Parameter values greater
than the specified limit are set to the maximum allowable value for that
parameter. If a CO (7–bit) control character is received within a control
sequence, the control character is executed by the printer as if it was received
before the control sequence. Parsing then resumes. The exceptions to this
rule follow:
• When the control character is <CAN> (18H) or <SUB> (1AH), the
sequence is aborted and the control character processed.
• If the control character is ESC (1BH), the sequence is aborted and a new
sequence begins.
• If a C1 (8–bit) control character is received within an escape or control
sequence, the sequence is aborted and the C1 control character is then
processed, if it is applicable to the printer. If not, it is ignored.
• When the (A0H) character is received within a control sequence, it is
processed as a <Space> (20H) character, and parsing then resumes.
• If character (FFH) is received within a control sequence, it is processed
as a <DEL> (7FH) character, then parsing resumes.
• When a GR character is received during a control sequence, the eighth
bit is ignored. The remaining seven bits define a GL character.
The following messages explain error codes that might arise when using the
single shift control character:
• If a C0 or C1 control character is received after a single shift control
character <SS2> (8EH) or <SS3> (8FH), the control character is
processed and the single shift flag remains set. If a control sequence is
received after <SS2> (8EH) or <SS3> (8FH), the sequence is processed
and the single shift flag remains set.