Rockwell Automation 1395 Multi-Comm Hardware/Software - Manual (Page 32)

Chapter 3
Configuration & Interfacing
3–21
If the normal run speed reference is selected, the PLC Controller must send
a 16 bit word to External Vel Ref (parm 154) in the Drive. Because the
speed reference is a complete 16 bit word, the PLC Controller must send
the data as a complete word rather than as individual bits as was the case
for logic command bits. In this example, word 1 of integer file N10 is used
to store the speed reference for the Drive. The MOV block in rung 6 of
Figure 3–14 transfers the 16 bit word of N10:01 to word 2 of the output
image table. Because word 2 of the output image table is sent to parameter
308, which in turn is linked to parameter 154 (Figure 3–13), the 16 bit
word N10:01 is the speed reference input to the Drive parameter 154.
Information transferred back to the PLC Controller from the Drive is
handled much as it was in the previous example, with the exception that
data is transferred from the input image table of the PLC Controller to the
working data files in the PLC Controller program. Again, note that bit
coded words such as Logic Status (parm 100), are bit numbered in Octal in
the PLC Controller, while the Drive is in Decimal.
PLC Controller Block Transfer
In addition to using the I/O image table of the PLC Controller to transfer
data to the Drive, there are certain times when it is desirable to transfer
data on a non-time critical basis, or in larger blocks. The MCA board
allows this to be done through RIO by using the block transfer mechanism
of the PLC Controller. It can also be done using the DH+ protocol which is
explained later. For example, if several parameter settings need to be
changed based on the type of material being produced on a machine, the
block transfer mechanism would be a good choice.
The block transfer function does not directly use any of the Discrete I/O
slots in the rack. However, the MCA board places several bits in the PLC
input image table to transfer the Adapter status information. This status
information is used in the PLC program for proper sequencing of the block
transfer instructions. The status information must be updated at the same
rate as the discrete I/O , therefore, the Adapter reserves the first word or
group in the rack for this information. Also, the first word or group in the
PLC Controller output image table is reserved for block transfer use.