Siemens LOGO!, Руководство пользователя

Страница: 267 / 534

LOGO! functions
4.4 Special functions list - SF
LOGO!
Manual, 04/2011, A5E03556174-01
267
Functional Description
The mathematic instruction function combines the four operands and three operators to form
an equation. The operator can be any one of the four standard operators: +, -, *, or /. For
each operator, you must set a unique priority of High (H), Medium (M), or Low (L). The high
operation will be performed first, followed by the medium operation, and then by the low
operation. You must have exactly one operation of each priority. The operand values can
reference another previously-defined function to provide the value. The mathematic
instruction function rounds the result to the nearest integer value.
The number of operand values is fixed at four and the number of operators is fixed at 3. If
you need to use fewer operands, use constructions such as + 0 or * 1 to fill the remaining
parameters.
You can also configure the behavior of the function when the Enable parameter En=0. The
function block can either retain its last value, or be set to 0. If the parameter Qen → 0 = 0,
then the function sets AQ to 0 when En=0. If the parameter Qen → 0 = 1, then the function
leaves AQ at its last value when En=0.
Possible errors: Zero division and overflow
If the mathematic instruction function block execution results in zero division or overflow, it
sets internal bits that indicate the type of error that occurred. You can program a mathematic
instruction error detection function block in your circuit program to detect these errors, and to
control the program behavior as needed. You program one mathematic instruction error
detection function block to reference one specific mathematic instruction function block.
Examples
The following tables show some simple example mathematic instruction block parameters,
and the resulting equations and output values:
V1 Op1
(Pr1) V2 Op2
(Pr2) V3 Op3
(Pr3) V4
12 + (M) 6 / (H) 3 - (L) 1
Equation: (12 + (6 / 3)) - 1
Result: 13
V1 Op1
(Pr1) V2 Op2
(Pr2) V3 Op3
(Pr3) V4
2 + (L) 3 * (M) 1 + (H) 4
Equation: 2 + (3 * (1 + 4))
Result: 17
V1 Op1
(Pr1) V2 Op2
(Pr2) V3 Op3
(Pr3) V4
100 - (H) 25 / (L) 2 + (M) 1
Equation: (100 - 25) / (2 + 1)
Result: 25