Thread Starter

Glen Turner

Imagine my horror, so if I want to add anything to the scanlist I have to bring down all devices on the network and shut down the process. Gee AB has really dropped the ball on this one. Please, someone tell me this isn't true?

Eddie Willers

You can't add racks to a RIO channel in run mode either, so it's no great change to the PLC-5 modus operandi. It sure would be nice to have the DeviceNet scanlist in the PLC instead of in the module, especially for DCS-like systems, but that's not the way it is.

All A-B DeviceNet scanners use nonvolatile memory to store the scanlist, so when you change the scanlist the module has to go through a reset to save it to flash. You'll see it display code 95 during the couple of seconds it saves to FLASH.

The PLC itself doesn't have to be in PROG mode; only the first bit in the command word for the module has to be zero. Subtle but important difference.

If you have to change a DeviceNet scanner scanlist but can't shut the process down, you can send messages to all of your slave devices to set their DeviceNet fault reaction to "hold last state", then go ahead and disable the 1771-SDN and change the scanlist. It's a lot of work, but it's principal way I've seen to work around the flash memory save cycle.
Thanks for the tip, and sure you are right about the RIO but if you have enough spare I/O in your rack it's easy to add another motor or device without having to reset anything.
It is true you have to stop devices on the network however the processor does not have to be put into program mode. You can turn to scanner off by toggleing a bit in the BTW transfer word. I only get one shutdown a year and have 7 networks installed but with advance planning and adding a few extra nodes of various types this has not been a problem.