====== Using Ladder Logic I/O ======

Cubloc I/O ports can be used by both BASIC and Ladder Logic. Without
defined settings, all I/O ports are controlled in BASIC. The UsePin
command must be used to set the I/O ports for use in Ladder Logic.

   UsePin 0,IN
   UsePin 1,OUT

The above code sets P0 as input and P1 as output for use in Ladder Logic.
Those ports declared with the UsePin command will be re-flashed during a
ladder scan. Re-flashing means that, prior to a ladder scan, those ports
declared as IN with the UsePin command will have their input read and
copied to the port's corresponding P register. 

After the ladder scan, those
ports declared as OUT with the UsePin command will have the
corresponding P register's value written to the port's output.

{{ :cubloc:using_i_o:ladderscan.png?nolink |}}

In BASIC, the commands In and Out an be used to control I/O ports. This
method directly accesses the I/O ports when reading and writing. 

In order to avoid collisions between the two, I/O ports should be used in either
BASIC or Ladder Logic, but not both. Once a port is declared with the
UsePin command, it can only be used in Ladder Logic and cannot be
directly accessed in BASIC, except through the ladder registers.

   UsePin 0,IN, START
   UsePin 1,OUT, RELAY

Aliases (such as START or RELAY as shown above) can be assigned using
the UsePin command to improve readability.

===== Use of Aliases =====

When creating Ladder Logic using "Register numbers" such as P0, P1, and
P5, aliases can be used to help programs.

{{ :cubloc:using_i_o:ladderalias.png?nolink |}}

In order to use an alias, they must be declared in BASIC.

<code xbasic>
Usepin 0,In,STARTKEY
Usepin 1,In,SW1
Usepin 5,Out,MainMOTOR
</code>

or

<code xbasic>
Alias P0 = STARTKEY
Alias P1 = SW1
Alias P5 = MainMOTOR
</code>

Aliases can be declared using either the UsePin or the Alias commands

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