Rockwell Automation Publication MOTION-RM002H-EN-P-February 2018 525
Use different control words on all MDAC instructions. If the same control word
is used for the active and pending MDAC, the IP bit of the pending MDAC will
not work properly. When separate axis control words are used for the active and
the pending MDAC instructions, the active and the pending MDAC will both
have their IP bits set. However, only the active MDAC will have its AC bit set.
This is standard operation for all instructions. No detection of the same control
word used on multiple instructions is made.
Master Reference
The Master Reference for an MDAC instruction selects the Master Axis position
source.
The enumerations for Master Reference Axis are:
Actual – Slave motion is generated from the actual (current) position of the
Master Axis as measured by its encoder or other feedback device.
Command – Slave motion is generated from the command (desired) position of
the Master Axis.
Because there is no Command Position for a Feedback Only Axis, if you select
either Actual or Command for Master Reference, the Actual Position of the
Master Axis is used. The Actual and Command Position are always the same for
this case. No error is generated.
Because there is no Actual Position for a Virtual axis, if you select either Actual or
Command for Master Reference, the Command Position is used. No error will be
generated. An error is generated if a MDAC instruction is executed that changes
the Master Reference of a slave axis that is in motion. The new MDAC
instruction will error and the original one will remain active.
Structured Text
Operand Type Format Description
Source SINT
INT
DINT
REAL
STRING
structure
tag Initial element to copy
Important: the Source and Destination
operands should be the same data type, or
unexpected results may occur
Destination SINT
INT
DINT
REAL
STRING
LINT
structure
tag Initial element to be overwritten by the
Source
Important: the Source and Destination
operands should be the same data type, or
unexpected results may occur
Length DINT immediate or tag Number of Destination elements to copy
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