INFICON STC-2000A Thin Film Deposition Controller Operating Manual - Manual (Page 168)

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STC-2000A DEPOSITION CONTROLLER
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Another usage is to re-program some of your relays quickly. Just use the soft nodes as
intermediate outputs of your rungs. Then you can have a simple rung that Inputs a Soft Node and Outputs
it to a relay. There is an example later in this section of doing this.
Synchronize Events
There are 30 events (ID#s 170 to 199) that have a special use with the computer interface. They
can be set with commands through the computer. In this manner, you can synchronize events in the STC-
2000A with an external computer via an active I/O program.
Internal Operations
The way the STC-2000A interprets an I/O program is useful to know, especially when writing
complicated programs. The way variables and functions are evaluated is by using
what is called a stack. By using this method, parentheses are not needed to specify
order and use of operations. Each item that is entered into your program will either
push something on the stack, pop it off, or modify the stack contents. The variables
are evaluated to be either true or false (or a scalar value if of M or V types) and that value is used. Let us
look at the following rung and see how the stack works. Refer to Table 5.4, for what the ID numbers refer
to.
SECTION 5.8
Stack Operation
I0 I1 ! ¦ O8
Scanning Tokens
The way this is read is: do an input function on ID #0 (remote input #1), do an input function on
ID #1 (remote input #2), complement what is on the top of the stack (the state of remote input #2 in this
case), do an 'OR' operation, and output the result to ID #8 (relay #1).
Assume That The Variables I0 And I1 Are Both False. As the rung gets evaluated, the stack
will look like this.
I0
F
-
I1
!
¦
-
O8
F T T
- F F -
a b c d e
Figure- 5.2: Stack I/O Operations.
The lines indicate the movement of the stack. A downward slope of the lines in Figure 5.2
indicates a push operation and an upward slope indicates a pop. Notice that when the rung is completely
evaluated, the stack is empty (Figure 5.2e). The stack in this example has a depth of only 2 objects, but the
STC-2000A has a much larger stack. Because you cannot enter a rung longer than a line on the display, it
is not possible to exceed the depth of the stack.
Each token within the rung is scanned, and each rung is scanned. All of the rungs are scanned 10
times per second. An input function causes the evaluated variable to be pushed on the stack. An output
function will cause the stack to be popped. The value that is taken off of the stack is used as the output.
The 'AND', 'OR' operators will pop 2 values off of the stack, do the operation, then push the result back on
the stack. The 'NOT' operator will pop 1 value off of the stack, reverse the state of it, then push it back on.
Likewise, all the other arithmetic, relational and selection operators perform similarly (see chart). The stack
is always empty when the STC-2000A starts to evaluate a rung, and must be empty when it finishes
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