Communications Errors
=====================

HUNTER provides a range of communications error messages to warn the
user of failure situations. The error messages are designed to be
trapped by the Basic :doc:`../basic-functions/on-comms`
statement and handled by the user's program.

However, the errors can occur when HUNTER is under manual control (for
instance, in TERM mode) or if the user's application does not contain ON
COMMS. In this event, HUNTER will display:

::

   * * * Communication Failure * * *

               -- Error nn --

where nn is the Error number. The attempt at communication can be
aborted either by powering the HUNTER off or by pressing ENTER, in which
case control is passed back to the DEMOS file manager.

The available error messages are:

Error 01: Unanswered line bid
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This is due to not receiving any reply in a request for the line,
usually caused by incorrect connection of the communications channel.
(Synchronous mode only).

Error 02: No response from receiver
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

After establishing the line, a buffer has been sent to which no response
has been given, despite 10 ENQs having been sent. (Synchronous mode
only).

Error 03: Response not matched by odd-even block count
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The wrong positive acknowledgement has been given to a buffer, despite
confirmation requests. (Synchronous mode only).

Error 04: Retransmission rejected
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Repeated transmission of a buffer gets only the NAK response, has tried
10 times. (Synchronous mode only).

Error 05: Loss of response from receiver.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

No ENQ has been received in reply to a WACK (synchronous mode only).

Error 06: Not used.
^^^^^^^^^^^^^^^^^^^

Error 07: Not used.
^^^^^^^^^^^^^^^^^^^

Error 08: Receive timeout Error
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

No data has been received to a request for input (e.g.
:doc:`../basic-functions/linput`) for the specified time.

Error 09: Transmit timeout Error
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Transmission has not been able to take place for the specified time.

The error number is available in the location COMERR (see
:doc:`../appendix/memory-locations`).

Error 10: ETX/ACK timeout Error
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

No response has been received for 30 seconds.

Error 11: ACK/NAK failure
^^^^^^^^^^^^^^^^^^^^^^^^^

Three attempts have failed to get an ACK.

Error 12: Systime failure
^^^^^^^^^^^^^^^^^^^^^^^^^

Ten re-transmissions have failed to get an ACK.