COAX COMMUNICATIONS BUFFER
In the SCS mode, if ML defines a position beyond the end of the
buffer, data wraps from the end of the buffer back to address
(X'0050') which is the beginning of the data area.
In the DSC mode, if ML extends beyond the end of the buffer,
printing stops at the end of the buffer. An End of Message (EM)
control code in the buffer overrides the ML, terminating the print
process at that point in the buffer.
When set correctly, the printer processes characters from the
message buffer, starting at the MSA and continuing in a
sequential manner for the length of the message. This
processing prints the printable characters in the buffer, using any
commands also in the buffer to format the printed page as
required.
When a print order has been completed, the Xerox MRP Family
coax printers return an ‘Order Complete’ in the PCIA byte
X'0000' and posts the response ‘Printer Status Available.’
DSC print order processing
In DSC mode, the message buffer contains DSC codes for
printable characters and control functions.
Following the printing of the last line of data in the buffer, an
automatic new line is performed unless the print position is
already in column one or the DSC options of the 4220/MRP or
4230/MRP coax printer have been set to inhibit this action.
The maximum print position (MPP) from PCIA byte X'0018'
specifies the maximum print position for each line of print. If
MPP is zero, the print line width is determined by the value set at
the printer control panel.
If an entire print line does not contain any printable characters
(all are nulls, attributes, or in a nonprint field), it may not be
printed depending on how the Null Suppression option is set in
the 4220/MRP or 4230/MRP coax printer. To print a blank line, at
least one character in the line must be a space character within a
print field, or the Null Suppression option must be disabled.
Invalid control codes are treated as nulls.
In addition to the printer control codes, the data may contain
screen-field attribute characters because the printer can be used
as local copy printer (copy screen image to printer). A field
starts with a field attribute (FA) character and ends with the next
FA character. Fields that cannot be printed (for example, input
fields) are treated as blank fields and are called nonprint fields.
The FA is normally the first character in a print order. It is
defined in table D-4.
D-8 XEROX MRP FAMILY COAX COMMAND REFERENCE