Asynchronous Terminals and Printer Processes Programming Manual

PRINTER PROGRAMMING CONSIDERATIONS
Error Handling
DATA PARITY ERROR Recovery
The I/O process can perform automatic parity error recovery for
the 5520 printer. If a parity error is detected, the software
attempts to recover unless one of the following conditions
exists:
• A parity error persisted after the retry count was exhausted.
• A parity error occurred while the device was off line (DEVICE
NOT READY or PAPER OUT).
• A parity error occurred on a request for status immediately
following a write of data, or a parity occurred in the data.
• A parity error occurred during a write of data that contained
embedded control characters.
Do not include control characters %00 through %37 in data sent
to the 5520 printer because they disable parity error recovery.
The I/O software provides the appropriate line termination and
all escape sequences. The 5520 recognizes the following control
characters: %12 (line feed), %14 (form feed), %15 (carriage
return), and %33 (escape). Any other control characters are
printed as spaces. The escape character is the first character
in all escape sequences.
Any unrecognized escape sequence sent to the printer is assumed
to be five characters in length. The printer converts an
unrecognized escape sequence to blank characters before printing
the line.
DEVICE POWER ON Error
If the printer power fails and then powers up again, the contents
of the DAVFU and all data in the printer's internal buffers
(approximately 1K bytes) are lost. The printer powers on in an
offline state, and the DAVFU is reloaded with default values.
If the printer goes offline because of a paper out, cover open,
or other correctable fault and then comes back online, the
contents of the buffer will print. Then printer then waits for
more data.
File-system error 100 (DEVICE NOT READY) will first be returned
to the application. If the power on occurred while the file was
open, error 191 (DEVICE POWER ON) is returned after the printer
has been placed online.
7-14 November 1987