~JN - Head Test Fatal
Turns the printhead element test on, so that a failed element halts the printer.
~JN is a switch, not a test run. It turns the printhead element test on, and the
printer then halts the first time it detects a failed element.
Syntax
~JNSupport
Accepted and skipped, because it configures the printer rather than the label. It cannot change the rendered output, and Labelary skips it too.
The command enables a hardware self-test, and no printhead exists to test. The renderer does not parse this command. It reports IGNORED_COMMAND at info severity, which does not reach X-Warnings. Labelary is also silent, so the rendered label is identical in both engines. — not pinned by a test
Labelary renders this command.
Parameters
~JN takes no arguments.
Behavior
That state is sticky: after the printer sees an element failure, it stays in error
until ~JO turns the test off or the power cycles. The guide adds a caution: the
printer cannot receive data when the communications buffer is full, so the ~JO
that clears the condition never arrives.
^JT schedules the test; ~JN and ~JO only decide whether a failure is fatal.
This API has no printhead to test, so the renderer ignores this command.
Differences from the specification
Labelary against the ZPL II guide
Where Labelary — our compatibility target — behaves differently from the printed specification.
- Labelary describes
~JNas a printhead test. The guide describes it as a switch: it turns the head test option on, and the printer then halts when it detects an element failure. A render shows no difference, because neither implementation performs a test. — not pinned by a test
Example
The test made fatal ahead of a label. The label renders exactly as it would without the command:
^XA
~JN
^FO50,50^A0N,40,40^FDHead test fatal^FS
^XZ
Related commands
~JOHead Test Non-FatalTurns the printhead element test back off, so a failed element no longer stops the printer.^JTHead Test IntervalSchedules how often the printhead element test runs, and which elements it covers.~HQHost QuerySends one of ten named printer reports back to the host.