INFICON STC-2000A Thin Film Deposition Controller Operating Manual - Manual (Page 160)

p
STC-2000A DEPOSITION CONTROLLER
y
Boolean Operations
SECTION 5.2 Boolean Definition
A basic understanding of Boolean operations is needed before you can write an I/O program. A
Boolean variable has only 2 states. This can be thought of as on and off, closed and opened, 1 and 0, active
and inactive, or true and false. Only the terminology is different for these examples. The important thing
to keep in mind is that there can be only 2 states.
Boolean Operations
There are 3 basic operations that you can do with Boolean variables. These are 'ANDing', 'ORing',
and 'Complementing' (complementing is also known as the 'NOT' operator). For the 'AND' operator, both
input conditions must be true for the output to be true. If you are familiar with relays, this is like putting 2
relays in series with each other. Both relay switches must be closed for the output to become active.
switch 1 switch 2
For the 'OR' operator, either input condition being true will cause the output to become true. In
terms of the relay description, either one of the switches (or both of the switches) can be closed to activate
the output.
switch
1
switch
2
The 'NOT' operator is only used on one input condition. It outputs the reverse state of the input. This is
like using the normally closed (instead of the normally open) contacts of a relay, converting true to false,
on to off, off to on, etc.
Figure 5.1 illustrates using relays and the way the STC-2000A represents their function. Many people like
to first write out their solution using relay notation, then translate each rung for the STC-2000A's notation.
Relay Ladder Notation
I0 I1 I2 && O8
I0 I1 & I2 & O8
OR
I2 I1 I0
I0
O8
I0 I1 ¦ O8
I1
O8
Figure- 5.1: Relay Ladder Notation [top is 'AND'ing, bottom is 'OR'ing]
SECTION 5.XX page 160 of 292