问答系列（三十六） 点击：1567 | 回复：0
发表于：2002-11-04 09:22:00
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How is each field device addressed and how do you troubleshoot the component?
Answered by Ray Romito, DeviceNet Trainer,
e-mail:
A210) I would encourage you to browse around on www.odva.org and look at the technical overview information that is off the "Tech Info" tab, under Technical Information. (click on "DeviceNet Technical Overview - technical overview written for a technical audience. Also appears in the DeviceNet Product Catalog")
Every device on DeviceNet has a unique node address in the range of 0-63. If a node is added to the network that has the same address as another node it will not be allowed on. The spec allows for devices that have switches to set their address or that are software settable. In the case of switch settable nodes you would simply set the switches according to the address you want. For nodes with software settable node addresses the node will default to address 63 upon initial (out of box) power up. A commissioning tool would then be used to address the new node and adjust its address. Once adjusted to the new address the node will assume that address from then on, even if power is cycled (implies there must be non-volatile storage for this).
When commissioning a system of software settable (node address) nodes, you would normally add nodes to the network one at a time, adjusting the address of each one before adding the next. The spec defines a method of communicating with nodes that have duplicate node addresses, but not all devices (or commissioning tools) support it. This method is called "Faulted Node Recovery", which uses serial number and vendor ID to distinguish one duplicate addressed node from the next. The only function that can be performed in this manner is to adjust the node address. You still need to go to each node one at a time, but they don^t have to be added to the network one at a time. You didn^t ask, but similarly the baud rate can be switch selectable, software selectable or automatically detected via additional hardware on the device. Once the baud is set (as opposed to acquired via auto baud detection) it will remain at that baud rate even after power up, just like the node address. Autobaud devices may auto detect each time they power up, and in fact, probably would desire to do that.
Troubleshooting a device on the network is going to be largely dependant on what^s wrong and what the manufacturer decided to make available via the network. Assuming that the device is capable of talking and does indeed respond to requests, there are network configuration tools that can address where the "what did the manufacturer make available" question is significant. Some companies provide very little in the way of diagnostics, while others provide a great deal. It^s hard to answer more specifically than that. If the device is not communicating, or not doing so reliable, then troubleshooting becomes more involved and is probably best described in the document found on the ODVA web page. Visit the "Downloads" tab, Technical Papers, "How To Implement (and troubleshoot) a DeviceNet Network"
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