<P>Hi,
<BR>It's a little different among mfg's , but generaly like this:</P>
<PRE>
-------------------------------------------------
X1 X2 Y1
----| |-----|/|-------( )
You need input X1 AND NOT X2 to get output Y1
-------------------------------------------------
X1 Y1
----| |--!------( )
|
X2 |
----| |--!
You need input X1 OR X2 to get output Y1
-------------------------------------------------
X1 X3 Y1
----|/|--!--| |--!--( )
| |
X2 | X4 |
----| |--!--|/|--!
You need (NOT X1 OR X2) AND (X3 OR NOT X4) to get Y1
</PRE>
<P>For the simplest functions. Som mfg's have a lot of special instructions and then you have to read the manual.</P>