Description Ssi_Absolute_Encoder - Siemens SIMATIC ST-1500 Function Manual

Using the SSI_Absolute_Encoder technology object
4.5 Programming the SSI_Absolute_Encoder
4.5.3

Description SSI_Absolute_Encoder

Description
The SSI_Absolute_Encoder instruction is used to control the position input and measuring
functions of the technology module TM PosInput via the user program.
Call
The instruction must be called once per channel, either cyclically or in a time-controlled
program. The call is not permitted in an event-controlled interrupt program.
Operating principle
Position value: The position value is available at the output parameter PositionValue. The
position value is updated every time the instruction is called.
Measured value: The technology module updates the measured value asynchronously to the
instruction call based on the configured update time. The measured value last determined by
the technology module is updated at the output parameter MeasuredValue each time the
instruction is called.
Measured value and position value are available in parallel as output parameters.
Instead of a measured value, the complete SSI frame can be returned at the output
parameter CompleteSSIFrame. Either MeasuredValue or CompleteSSIFrame is valid,
depending on the parameter assignment.
Capture: The output parameter CaptureStatus = TRUE indicates a valid Capture value at the
output parameter CapturedValue.
● A Capture value is captured under the following conditions:
– A digital input has the parameter assignment "Capture"
– CaptureEnable = TRUE
– Edge at digital input with the Capture function
● The output parameter CaptureStatus is reset by a negative edge at the input parameter
CaptureEnable.
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Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG