ON COMMS
========

Function
--------

**ON COMMS** allows communication errors (typically a protocol failure)
to be handled by the user’s application program.

Syntax
------

ON COMMS GOTO [line no]

or

ON COMMS OFF

Examples
--------

::

   ON COMMS GOTO 1000

   ON COMMS OFF

Remarks
-------

The statement operates in a similar manner to :doc:`on-power`.

When a communications error is detected, control is returned to the
Basic Interpreter. Execution continues from a defined line number
specified in the Basic program.

In order to allow normal communication error messages the statement ON
COMMS OFF disables this mode. The byte of memory ``COMERR`` is available
to the programmer and contains a code which represents the type of error
which has occurred in the communications. The available codes and their
meaning are described more fully in :ref:`communication-error`.

In a typical application, ON COMMS would be used to present the Operator
with a plain language statement of the form:

"Communications have failed. Please re-dial and try again".

Re-tries or repeat blocks can also be controlled by the user program, as
required.