ladder logic

-| |- examine-if-open
-|/|- examine-if-closed

you can thank rockwell for that.

-( )- output bit

ladder reads left to right then down.

thats pretty simple, huh?
I'm sure there's heaps of tech books that can help further - or even a short course part-time would be beneficial.
<BR>It's a little different among mfg's , but generaly like this:</P>
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

<P>For the simplest functions. Som mfg's have a lot of special instructions and then you have to read the manual.</P>