Chapter 9
168
Logic programming – Function blocks
Truth table for the User mode switch function block
The truth table uses the following designations:
“0” means logic Low.
“1” means logic High.
Inputs Outputs
1 2 3 4 5 6 7 8 Fault present 1 2 3 4 5 6 7 8
10 0 0 0000 0 1 0 0 0 0 0 0 0
01 0 0 0000 0 0 1 0 0 0 0 0 0
00 1 0 0000 0 0 0 1 0 0 0 0 0
00 0 1 0000 0 0 0 0 1 0 0 0 0
00 0 0 1000 0 0 0 0 0 1 0 0 0
00 0 0 0100 0 0 0 0 0 0 1 0 0
00 0 0 0010 0 0 0 0 0 0 0 1 0
00 0 0 0001 0 0 0 0 0 0 0 0 1
More than one input High or no input
High for shorter than the set
discrepancy time
0 = Last output combination
More than one input High or no input
High for equal or longer than the set
discrepancy time
1 = Error output combination
Sequence/timing diagram
If the inputs of the function block are connected to inputs of an safety I/O module
which are connected to test outputs, and the faulty input combination is the result of
a test pulse error (stuck-at-high) which leads to a Low input value, the test pulse
error needs to be reset first, e.g. by briefly interrupting the corresponding input line
or test output line.
If the inputs of the function block are connected to inputs of an safety I/O module
which are connected to test outputs, then a cross circuit between the used inputs is
detected only if a user mode is selected that activates one of these inputs.
Table 72:
Truth table for the User
mode switch function block
Figure 151:
Sequence/timing diagram
for the User mode switch
function block
Note
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