Single Bit Input Port
=====================

The single input bit has been implemented for use with devices such as
bar-code wands, voltage free switch contacts, etc. It is provided via
the 4 pin LEMO socket pin 2. Note should made be that it is shared with
the TXCLK on the V24 interface (pin5). It should not, therefore, be used
at the same time as the communications when hardware handshaking is in
use.

Circuit Implementation
----------------------

The input is configured as a protected, pulled up CMOS compatible line:

|Circuit Layout|

It has a logic 1 threshold of > 3.5V and a logic 0 < 1.5V. It is
protected to ±25V.

The pull-up resistor enables the use of a switch to ground to provide
the input.

No debounce circuitry is provided. If it is required then software must
be written for this purpose.

This is bit 3 on I/O port 2. See :doc:`port-allocations`.

Pin-Out of LEMO Connector
-------------------------

|LEMO Connector|

====== ============================
Pin No Signal
====== ============================
1      Ground
2      TX CLK or input
3      Charger/reset
4      5V output (Wand option only)
====== ============================

.. _lemo-connector:

LEMO Connector
--------------

The four pin LEMO plug is installed by aligning the red mark on the plug
sleeve with the corresponding red mark on HUNTER'S LEMO socket, the
square pin on the plug body must also align with the key-way on the
socket. The LEMO plug is then pushed firmly into HUNTER'S socket until
the outer sleeve of the plug is flush with the casing of HUNTER'S LEMO
socket.

Removal of LEMO Plug
--------------------

To remove the LEMO plug from HUNTER it is necessary to pull back the
spring loaded outer sleeve before pulling the plug out of HUNTER'S
socket.

.. |Circuit Layout| image:: circuit-layout.png
.. |LEMO Connector| image:: lemo-connector.png