User`s manual

1-4 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
1
The Series 90-30 PLC and the DSM314
The DSM314 and Series 90-30 PLC operate together as one integrated motion control package.
The DSM314 communicates with the PLC through the backplane interface. Every PLC sweep,
data such as
Commanded Velocity
and
Actual Position
within the DSM314 is transferred to the
PLC in %I and %AI data. Also every PLC sweep, %Q and %AQ data is transferred from the PLC
to the DSM314. The %Q and %AQ data is used to control the DSM314. %Q bits perform
functions such as initiating motion, aborting motion, and clearing strobe flags. %AQ commands
perform functions such as initializing position and loading parameter registers.
Besides the use of %I, %AI, %Q, and %AQ addresses, an additional way to send parameters from
the PLC to the DSM314 is with the COMM_REQ ladder program instruction. Details about
using the COMM_REQ instruction with the DSM can be found in Appendix B,
DSM314
COMM_REQ Instructions.
PLC Data Latency and DSM314 Latencies
The DSM314 is an intelligent module operating asynchronously to the Series 90-30 CPU module.
Data is exchanged between the CPU and the DSM314 automatically. For information about the
operation of the Series 90-30 sweep refer to the
Series 90-30 PLC CPU Instruction Set Reference
Manual
GFK-0467
. The following information specifies timing considerations as applied to the
DSM314 module.
PLC to DSM Data Transfers
•
PLC based functions may retrieve DSM status (%I and %AI) information from the DSM data
memory asynchronously. The DSM will internally refresh all status data except
Actual
Velocity
at the position loop rate (once every 0.5 to 2 ms).
Actual Velocity
is updated in the
DSM data memory every 128 milliseconds. The DSM performs averaging to generate an
accurate
Actual Velocity
reading; therefore, the
Actual Velocity
reading is not intended for
high-speed control purposes.
•
The PLC requires approximately 2-4 milliseconds back-plane overhead when reading data
(%I and %AI) from and writing data (%Q and %AQ) to DSM internal memory if the DSM is
located in the CPU rack. The PLC will normally read input data from and write output data to
the DSM once per PLC sweep. A worst case scenario is if the DSM internal data update
(which takes 0.5 to 2 ms to occur) occurs just after the PLC scan’s input update. The PLC
will not read DSM data again until its next scan. The result is that any changes in DSM data
will be available in the PLC either 4-6 ms later or approximately one PLC sweep later,
whichever is larger.
•
The VersaPro configuration software automatically selects the lengths of %AI and %AQ data
based upon the number of axes configured. A PLC CPU requires time to read and write the
data across the backplane with the DSM314. The
Series 90-30 PLC Instruction Set
Reference Manual,
GFK-0467 version M or later, documents the PLC sweep impact by CPU
model group when the different axis configurations are selected. Also refer to the Important
Product Information sheet that comes packaged with the DSM module.
•
PLC commands to the DSM (%Q, %AQ) are output to the DSM at the end of the PLC logic
solving sweep. The DSM will process the commands within 4 milliseconds after receipt..