DeviceNet questions

Hi Everyone,

Yesterday I started my final year project at college. I am working on an SMC-designed pneumatic assembly line which is networked (there are several stations) on DeviceNet. I'm just trying to familiarise myself with the idea of DeviceNet.

- The "main" PLC is a SLC-500 which uses a 1747-SDN scanner module.
- One other card is installed in this PLC's rack - it has 6 inputs and 6 outputs.
- There are more than 6 physical output devices on the conveyer system, such as one pallet stop on each of the eight stations)

I exported the main PLC's address/symbol list into Excel and determined the output addresses of the conveyer devices I need.

For example, station 1's pallet stop is addressed at O:1/32. This I translated to O:1.2/0.

Now some questions...

* How is it possible that the second word of the output card is somehow connected to this output, given that the output card only has 6 outputs? Must the SMC devices (pneumatic cylinders etc) be equipped with D/Net hardware?

*When the scanner module reads in the filed data, I gather that the data is transferred from the scanner's internal memory map to the SLC's M1 file. Likewise, the outputs from the SLC are mapped within the scanner's internal memory. What are the options for mapping?

I'd appreciate some guidance. I've read the manual for the 1747-SDN module but haven't really grasped the concept of addressing of a network.

Thanks in advance.

Richard Byrne. (hopefully soon to be EE. Technologist)

Richard,

Which model of SLC500 are you using? 5/03, 5/04, 5/05?
What slot is the 1747=SDN located in?
What slot is the 1746-IO12 care located in?

If I understand your post correctly, I'm going to assume that the SDN is in Slot 1. If that is the case then there is a really simple explanation: The address O:1/32 is an address in the SDN card, not the IO12 card. If you have the SDN card in slot 1 then you have 32 input words and 32 output words in that slot - I:1.0 to I:1.31 and O:1.0 to O:1.31. Writing to these addresses will turn on devices on your device net. Is the D-Net alrady configured for your lab? I'm wondering because you said you exported the address symbol list. Were you given a framework file to work from? If its already set up then all the I/O words for slot 1 are mapped to the physical points (air valves & sensor) on the DN and all you need to do is develop the program.

In RSLogix 500 open the O file and the I file. Are there 32 words at I:1.xx and O:1.xx and just one word at I:2.0 and O:2.o?
Open the IO configuration at the top of the project tree under controller and see what is each slot.

Or, if you have a file, zip it and attach it.

Alaric,

Thanks for the prompt reply.

Some details I neglected to reveal, but you assumed correctly - the SDN is in slot 1, the I/O card is in slot 2.

DeviceNet is already wired and configured. I'm using the factory-shipped programs to learn what I need.

In RSLogix 500 open the O file and the I file. Are there 32 words at I:1.xx and O:1.xx and just one word at I:2.0 and O:2.o?
Open the IO configuration at the top of the project tree under controller and see what is each slot.

Click to expand...

Yes and Yes. I assume that this means that I:1.xx and O:1.xx are in the scanner, and I:2.0 and O:2.0 are the inputs/outputs on the IO card? From looking at the address/symbol list, I see that the IO card controls an alarm light and the contactor for the conveyer motors among other things - which explains why when the SLC was in PROG mode, the contactor controlling power to the AC drive wouldn't pull in! - but that's a different story.

Is it likely then that the SMC pneumatic equipment is D/Net-connected? Are inputs read by the scanner read into the SLC in the same bit order?

Thanks again,

RB

RB,

(1)The 1747-SDN could be connected to DeviceNet inputs, or it could be connected to another SLC at a Remote I/O rack.
(2)Once the SDN module feeds I/O into the PLC, they act exactly like any other I/O.

Thanks.

After re-reading the 1747-SDN manual it is apparent that the scanner module acts like another I/O card - except instead of physical outputs it uses an image table.
The bits that correspond to each physical output device on the system are energised to change the state of the output.
The word sent out by the scanner (strobe message) apparently contains bits that control each of the up-to-64 devices to be controlled.

RB

Since my system has output address on the D/Net that include O:1/112 and O:1/145, I am assuming that it uses the DeviceNet output data from the SLC's M0 file. The reason I say this is that O:1/145 actually means O:1.9/1. I thought there were only 4 words in the scanner's discrete I/O data table (bits 0-63), which would not allow the O:1.9/1 since tis requires the ninth word.

Is my reasoning correct or am I totally confused.

RB

RB,

There are a full 32 words of output data and a full 32 words of input data. Not 4 words. In a SLC the output image table is dynamically configured at compile time - its not limited to a fixed size like on the PLC/5 or some other PLCs. Some cards use only 1 word. Some only 2. Some use 16 words. The SDN uses 64 words (32 in, 32 out). You shouldn't have to use M files - you dont need to use a block read/write on this card.

When the device net was preconfigured, each of those 32 words were mapped to a device on the network. Someone went into the device net scanner using RSNetworx software and told it to send some bits in the output image table to node on on the device net, other bits to node 2, etc, and how often to update those bits. For example, words 1 and 2 might be mapped to the SMC pneumatic valve assembly. The contents of these two words are transfered at the configured update rate over the Device netork to the SMC valve assembly - which containts a device net slave controller. This would allow you to transfer 32 bit of data to the valve assy. (Your actual valve assembly might be different, this is just an example). So if you clear bit O:0/24 and set bit O:0/33, then the module will update those words to the device net slave in the valve assembly. This slave will then respond to that data by turning off/on the appropriate valve. The slave doesn't know what the address is of the bits was in the PLC, it only knows it got 32 bits from the PLC and since it has 32 valves, it just matches each bit to the each valve in the assembly.

The SDN knows where to send the bits because it has been preconfigured for you, so you dont have to worry about mapping all the bits in the scanner to each of the different devices (lucky you, the hard part is already done).

With the device net preconfigured, you should be able to go online with the controler without any rungs in the program. With he controller in Run mode, you can open the O:1 file and directly turn on/off the bits to see the actual devices function.