Rockwell Automation 1757-ABRIO Process Remote I/O (RIO) Communication Interface Module - Manual (Page 145)

Publication 1757-UM007D-EN-P - December 2008 143
Appendix
C
Operational Comparison Between the
1757-ABRIO Module and a PLC-5 System
Normal Operational
Messages The 1757-ABRIO module is designed to respond, as much as possible,
like a PLC-5 system. In PLC-5 applications, all I/O modules are
physically configured for safe state if the PLC-5 controller is in
Program or Fault mode.
There is one important difference - the PLC-5 controller has
well-defined, built-in modes of operation, either program or run. The
1757-ABRIO module has additional modes due to increased
capabilities (see the table on
page 144 ). The 1757-ABRIO module uses
the concept of a tag to store data that is exchanged between the
1757-ABRIO module and controllers. A tag is a user configured data
array that is composed of data read from or written to I/O modules.
As long as any tag is being refreshed from a Read/Write generated by
a controller or from a DDE or OPC server, the 1757-ABRIO module
scans remote I/O in ACTIVE (Run) mode. In ACTIVE mode all block
transfers run and digital inputs and outputs update.
If all tags have timed out (have not been refreshed within the
configured refresh time), the 1757-ABRIO module indicates INACTIVE
mode. Inputs continue to be updated. Output modules are placed in
safe state via Program mode.
In AbRioCfg software, mode block transfers are held which causes the
analog modules to be set to configured safe state (usually Last, Min,
Max or Safe value). Digital outputs also do what they have been
configured at the rack to do - hold last state or shut-off.
While the PLC-5 controller immediately changes from program to run
or from run to program modes based on user input, the 1757-ABRIO
module has the ability to change between inactive to active when
communication with a controller is established. However, the change
from active to inactive occurs only after the longest time-out period
for any tag after the last tag has been updated by the host controller.