RS Networks for DeviceNet

dbh6

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Jan 2013
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Hello All,

I will be commissioning a devicenet network using RS networx for devices that are currently existing on an MCC. The devices are really just E3 plus solid state overload relay's each already having its own node address.The system is already up and running. The PLC is a control logix 5561 CPU with a 1756 DNB scanner module. I wanted to get a couple of things verified, and of course always make sure your wiring is correct, make sure your using terminating resistors at the furthest ends of the network to avoid reflections of waves, using a power supply rated for device net etc. The goal is to get the data from the devices to my scanner module which will then store data to my controller tags.

So here are my questions...all these questions pertain to RS networx's for device net.

1. RsNetworx for device net gives you the ability to upload from the network, their is a Network tab through which you can upload/download to and from the network. So i wanted to know what it means to download to the network what are you downloading to??

2. If you wanted to change the node address of the device assuming the appropriate dip switches or settings are set on the device to accept software changes, if you right click on any node you can change the node address, for the change to truly take effect do you have to power cycle your scanner module and the device or do those changes take effect on the fly??

3. For the scanner module to really go out and search the network you have to configure the scan list with the scanner. Having said that if you are in the scan list tab, their are a list of available devices on the left and by selecting the arrow to the right you can add all the available devices to the scan list. Once you do that their is a download to scanner button, which downloads the scan list to the scanner. So i want to know the difference between the download to scanner button which is in the scan list and the download to network option in the network tab.

4. Their was an instance when i downloaded to the scanner module and all the devices on the network faulted through which i fixed by power cycling the devices, do you know what might cause that?

5. Lastly, once i have the scan list configured and downloaded to the scanner, their is a Local:3:O.CommandRegister.Run bit through which you have to enable to get your scanner to browse the network is that correct?


That should be it, and of course if i have left something out that's vital please let me know.
 
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1. RsNetworx for device net gives you the ability to upload from the network, their is a Network tab through which you can upload/download to and from the network. So i wanted to know what it means to download to the network what are you downloading to??

First thing to get your mind around is that RSNetworx for DeviceNet is a configuration tool NOT an "online" browser, it only displays what it knows about the network. If you open an existing configuration file from your PC, you don't know if it is actually what is running in the devices on the network.

In other words, everything you do in RSNetworx is done "offline", and any changes you make have to be downloaded to each device, or the whole network.

RSNetworx can be used to update a single parameter on an online device, or an online device (all parameters), or all parameters for all devices on the online network, that is a download.

The parameter or configuration data can come from a configuration file stored on your PC (offline), or from the network itself (online).

IMHO, for an existing and working network consider the DeviceNet configuration file as a backup only, which could potentially be out-of-date with what is really configured on the live system.

When commissioning an existing network I will always go online and UPLOAD all devices from the network, that ensures my offline image of what is actually configured on the network is current.

2. If you wanted to change the node address of the device assuming the appropriate dip switches or settings are set on the device to accept software changes, if you right click on any node you can change the node address, for the change to truly take effect do you have to power cycle your scanner module and the device or do those changes take effect on the fly??

No - once you change the node address of a device that is capable of being configured dynamically, and sent that change to the device, it will remember it. I don't know of any devices that need a power-cycle to "fix" the new address. Power-cycling, however, is usually a requirement for devices that get their address from dip-switches, as they are usually only read on power-up.

But of course if you change the node address of a device that is already in the scanner's scan-list, you will need to make changes to the scanner's scan-list to accommodate the change, and I'm specifically talking about I/O mapping, it will not do it automatically. The device at the old address will be in error, and the device at the new address will not be scanned.

..tbc
 
3. For the scanner module to really go out and search the network you have to configure the scan list with the scanner. Having said that if you are in the scan list tab, their are a list of available devices on the left and by selecting the arrow to the right you can add all the available devices to the scan list. Once you do that their is a download to scanner button, which downloads the scan list to the scanner. So i want to know the difference between the download to scanner button which is in the scan list and the download to network option in the network tab.

Consider the scanner as just another device - but the configuration of this device enables data communication of the other devices into the PLC I/O tags/data-tables.

"Download to Scanner" is just the same as "Download to {any other device}" - in this instance you are only downlading the scan-list to the module (remember : RSNetworx is never actually "online").

"Download to Network" downloads every device with all parameters that RSNetworx currently holds for every device - don't use it unless you are certain it is appropriate to do so. One example of being "appropriate" is that you have multiple manufacturing cells with identical DeviceNet devices and configuration ... i.e. Copy/Paste.
 
4. Their was an instance when i downloaded to the scanner module and all the devices on the network faulted through which i fixed by power cycling the devices,

Welcome to devicenet !!
 
5. Lastly, once i have the scan list configured and downloaded to the scanner, their is a Local:3:O.CommandRegister.Run bit through which you have to enable to get your scanner to browse the network is that correct?

Nearly correct - this bit appears to "enable" or "disable" the devicenet by turning this bit on or off.

But it's more about output control, the devices are still scanned.

With the bit turned off, all devices should turn their outputs off.

Inputs, however, may or may not be disabled, some do some don't, it depends how the device was made.

I've yet to come across a DeviceNet network that needs to be turned "off", so I've always seen a single rung in the PLC program that has an unconditional OTE for the network RUN bit.
 
I wrote up a really long and detailed response to all of those questions but somehow it didn't post correctly. Darnit ! Daba, as usual, has good explanations.

#4 was probably due to the way A-B drives and motor controllers work with network connections. This goes way back to the 1336+ AC drives on RIO, and I'll say "drive" below where I mean "motor drive, overload relay, or most I/O devices".

The drives can detect two different network failure modes: a Connection Fault or a Connection Idle state.

A Connection Fault happens when the data wires get disconnected or the drive stops getting periodic packets from the Scanner.

A Connection Idle condition happens when the .RUN bit goes false, or the PLC goes into Program Mode. The device is still getting packets, but they are of zero data payload length so it doesn't apply them to its output functions.

The safest and most conservative thing to do if there is a Connection Fault or Connection Idle condition on the network is to stop the drive and declare a Fault condition that needs to be reset. You can reset via network messaging, or a discrete input, or by cycling power.

The most common way I set my drives up is to Stop when there is a Connection Fault or a Connection Idle condition. They don't fault, but they do Stop.

You can also configure the devices to hold the last state, or to actually apply a command and reference when the Fault or Idle condition occurs.
 
Ken, i feel you pain thats why i always copy to a notepad if i have a long post

Another aspect i also realized is say you go to the properties of the device you want to configure. That device will have a parameters tab where their is a parameter for the Dnet setup. In there you can specify input and output assembly instances and depending on what you specify as your instances the data sizes may change. Now when you go to the properties for the scanner module and go to the Input and output tabs it will show your the mapping of the IO to your local PLC tags if you have configured a scan list. Each slot as you can call it is 32bits in lengths. So lets say for one of your devices it takes up 1 bytes in the first slot and then the another device takes up 2 bytes in the first slot and another device takes up 1byte. Obviously you would have to manipulate the data in your program by either copying that DINT data to SINT or something or using other methods to view them correctly otherwise the datas wont display correctly. So is their a way through which you can adjust the mapping so it would eliminate your need to adjust in your program?
 
Ken, i feel you pain thats why i always copy to a notepad if i have a long post

Another aspect i also realized is say you go to the properties of the device you want to configure. That device will have a parameters tab where their is a parameter for the Dnet setup. In there you can specify input and output assembly instances and depending on what you specify as your instances the data sizes may change. Now when you go to the properties for the scanner module and go to the Input and output tabs it will show your the mapping of the IO to your local PLC tags if you have configured a scan list. Each slot as you can call it is 32bits in lengths. So lets say for one of your devices it takes up 1 bytes in the first slot and then the another device takes up 2 bytes in the first slot and another device takes up 1byte. Obviously you would have to manipulate the data in your program by either copying that DINT data to SINT or something or using other methods to view them correctly otherwise the datas wont display correctly. So is their a way through which you can adjust the mapping so it would eliminate your need to adjust in your program?

If you accept defaults, I/O mapping shovels everything at byte boundaries which doesn't fit well with logix5000 tags.

Here's a method I recommend, as it suits most networks.

Map the byte I/O for a device into the mapping files at 2 x node number - that will allow for 8 bytes of I/O per device, which is well within most devices. If a device needs more than 8 bytes of I/O data, then the next node address needs to be skipped.

Of course you have to do this mapping manually, accepting defaults puts your I/O data "messily".

Remember, you can only have maximum 64 nodes on each network, and node 0 is conventionally used by the scanner. Node 63 should not be used, because it is the default "out-of-the-box" node address for a device that is only software configurable. and Node 62 is most often reserved for attachment of an RS232 network interface module (dammit I forgot the part number)
 
@ daba

when you suggested "Map the byte I/O for a device into the mapping files at 2 x node number" how do i do this mapping manually?
 
@ daba

when you suggested "Map the byte I/O for a device into the mapping files at 2 x node number" how do i do this mapping manually?

uncheck the option for "map automatically" (default). I can't access RSNetworx right now, (wrong PC), so can't give details.

PM me if you can't see how to drive the mapping manually.
 
ahh ok i think i get it i don't have my PC right now but, since each slot is 32bits and by unchecking the option to map automatically and by assigning 2X the node number meaning each device will take up a slot each slot being 4bytes and by assigning 2 slots per device composing your 8bytes will lay it out better for data manipulation, i think thats what you mean't but correct me if im totally off
 
1. RsNetworx for device net gives you the ability to upload from the network, their is a Network tab through which you can upload/download to and from the network. So i wanted to know what it means to download to the network what are you downloading to??

Be very careful with the download to network option. I had a customer who replaced a DeviceNet sensor in the middle of the night and then selected download all to the DeviceNet network :sick: end result was 15 drives all set to defaults because their configuration had not been stored in the network configuration.

Unfortunately the machine builder had gone out of business and no backups were available, I had to re-commission all 15 drives and a number of other simpler nodes, that was a major task which took several days!

Whenever I go on-line with DeviceNet first thing I do is create a new backup by uploading all from network, this will upload all parameters from all nodes and then I save that setup with a new name.
 
Absolutely right, dbh6.

Having the devices manually mapped at 32-bit word boundaries eases data manipulation, as you said, and you always know where the data is for a particular device, just look in the interface tags at 2 x node number. Very easy to remember where the data is, and it makes documentation of the mapping locations largely unnecessary.

The length of the interface tags is 124 input and 123 output, so they will allow that mapping schema up to node 61, which is not a bad thing as 62 and 63 should be reserved as I mentioned earlier, so these node addresses need no mapping.

If and when you add any new nodes to the scanlist, you just have to remember to turn off that "Automap on add" option, as it is on by default. I can't find a registry value that configures it off by default.

Even if you choose not to map at 2 x node number, you can still align the mapping to 32-bit word boundaries - look at the "Options" buttons on the "Input" and "Output" tabs of the scanner dialog.
 
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