Power Warning
=============

When HUNTER'S batteries become exhausted a power warning message will
appear on the screen. Normal operation will continue, but keyboard
entries will be punctuated by warning tones and repetition of the power
warning message until the battery state is rectified either by
replacement of primary cells or recharging of Nickel-Cadmium cells, if
installed.

Eventually, if the warnings are ignored, HUNTER will shut down and
refuse to operate further.

Every HUNTER has to pass a stringent operating test in this low power
regime. However, it is strongly recommended that operator training
procedures and user programs are structured to avoid continued operation
when warnings become persistent, especially when rechargeable cells are
used.

The power warning sequence may be misleading if RS-232 communications
are used infrequently. When HUNTER'S communications system is activated
power drain increases significantly. This increase can cause the power
warning stage to be missed altogether, and instead cause HUNTER to shut
down without warning.

While this is not hazardous, it can be very confusing for an operator
who does not know what is wrong. Because of this it is recommended that
user programs with infrequent communication requirements use a test
routine. This activates the communications package, and then tests the
power state before restoring HUNTER to normal. This routine is used at
the start of every data entry sequence.

If batteries become exhausted whilst communications are in progress,
then normal power warning messages will appear once the keyboard
operation is resumed.

.. Note::

   Power warning messages only occur when keyboard entries are in
   progress.

Sample Warning Subroutine
-------------------------

::

   20 OUT 132,1
   30 J=INP(2):OUT 132,0
   40 IF J = 0 THEN RETURN
   50 CLS
   60 PRINT "PLEASE CHANGE MY BATTERIES!"
   70 BEEP: BEEP: BEEP: BEEP
   80 RETURN

This program operates as follows:

#. The power status is available as bit 2 in HUNTER port 2.

   0 = power OK, 1 = Low Power state.

#. Line 20 energises the RS-232 serial interface.

#. Line 30 reads the power state from port 2, and then closes down the
   interface to conserve power.

#. Line 40 checks the power status bit.

#. Line 50-80 Display a warning and ring HUNTER'S bell!