Hardware Characteristics
========================

Interface Connections
---------------------

HUNTER uses a standard communications line via a 25 pin "D" connector
compatible with the requirements of EIA specification RS-232-C. The
connections may be summarised as follows:

.. Note::

   HUNTER is configured as a 'DTE' Data Terminal Equipment.

.. image:: rs232male.png

=== ===================
Pin Description
=== ===================
1   Protective Ground
2   Transmitted Data
3   Received Data
4   Request to Send
5   Clear to Send
6   Data Set Ready
7   Signal Ground
8   Data Carrier Detect
9   (Not used)
10  5v Power Out
11  (Not used)
12  (Not used)
13  (Not used)
14  (Not used)
15  Transmit Clock
16  (Not used)
17  Receive Clock
18  (Not used)
19  (Not used)
20  Data Terminal Ready
21  (Not used)
22  Ring Indicator
23  (Not used)
24  (Not used)
25  (Not used)
=== ===================

Electrical Characteristics
--------------------------

HUNTER'S output voltages on signals "from HUNTER" are guaranteed to be
greater in magnitude then 5V when driving a 4K7 load in accordance with
EIA specifications. Typically output voltages are 8V in magnitude.

HUNTER detects input signals with a "fail safe" characteristic. Input
signals from -25V to +2.5V are detected as a logical ”1” or the mark
state. Signals from +3.5V to +25V are logical ”0” or the space state. On
the handshake signals the asserted state is spacing or logical ”0” e.g.
CTS.

To summarise,

Output:

| Logical ”0" or spacing Output > +5V with 4K7 load.
| Logical ”1” or marking Output < -5V with 4K7 load.

Input:

| Logical ”0" or spacing Input > +3.5V
| Logical ”1” or marking Input < +1.5V

Each input provides a line terminator impedance of 6K8.

Interface Power Control
-----------------------

Under normal circumstances the serial output interface is powered down
to conserve battery life. The first character which requires
transmission causes the interface to be powered up. A pause of
approximately 2 seconds is allowed for the interface to settle down and
then the character is sent. Further characters are not affected in this
way. Once powered the interface is latched on until HUNTER is switched
off or power removed using an :doc:`../basic-functions/out`
instruction in either Basic or machine code.

When the interface is powered up it may cause spurious characters to
appear to be sent out, causing problems with the receiving system. These
may be overcome by powering the interface, prior to requiring the data,
by sending any character as soon as HUNTER is switched on. A Basic
:doc:`../basic-functions/lprint` command will achieve this.

Alternatively, the interface may be controlled as follows:

::

   OUT 132,1

will turn the interface on and

::

   OUT 132,0

will turn the interface off.

If the interface is turned off after characters have been sent, then
further characters will not cause the interface to be powered up and
they will be lost.

Handshake Lines
---------------

The function of each of the handshake lines is described in turn in the
following section, with the exception of Ring Indicator (RI). RI is
provided to allow HUNTER to be switched on from an external source.