Rockwell Automation GMLC Reference Manual - Manual (Page 743)

Publication GMLC-5.2 - November 1999
706 Using the RIO Adapter Option
Other interlocks in the block transfer rungs can be required for your
application. At a minimum, you should have the following:
• A condition that causes the block transfers (don’t send block transfers
on every PLC scan).
• The enable bits (Bit 15 of the BT control block) of all other block
transfers in the ladder.
• The program running bit from the motion controller (SLC input 8;
PLC input 10), as shown previously.
The length of the BTW should always be set to zero, as shown. This
causes all 64 words of the data file to be sent to the motion controller. In
addition, continuous block transfers should not be used.
After the BTW requesting the data is sent, the next block transfer must be
a BTR to read the data. If not, the motion controller ignores the second
BTW, causing an error in the PLC. To ensure that the PLC and the motion
controller do not get out of sync with this write-read-write-read sequence,
interlock each block transfer with the enable bits (Bit 15 of the BT control
block) of all other block transfers in the ladder, as shown previously. This
ensures that the block transfers always occur in the order in that they
appear in the PLC ladder.
Interlocking the block transfers with the program running bit stops the
block transfers when the motion controller’s program is not running. This
significantly improves the downloading of GML Commander diagrams,
cam tables, etc., as well as the operation of the motion controllers built-in
setup menus. See Using the Dedicated Discrete Outputs in this chapter for
more information on the program running bit.
!
ATTENTION: The interlocks shown for the block
transfers are the minimum required for reliable operation.
Other conditions can be required in your application.