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Figure 28.6 A Devicenet Network

The network cable is important for delivering power and data. Figure 28.7 shows a basic cable with two wires for data and two wires for the power. The cable is also shielded to reduce the effects of electrical noise. The two basic types are thick and thin trunk line. The cables may come with a variety of connections to devices.

plc network -28.10

* bare wires
* unsealed screw connector
* sealed mini connector
* sealed micro connector
* vampire taps

Thick trunk -carries up to 8A for power up to 500m

Thin trunk -up to 3A for power up to 100m

Figure 28.7 Shielded Network Cable

Some of the design issues for this network include;

* Power supplies are directly connected to the network power lines.
* Length to speed is 156m/78m/39m to 125Kbps/250Kbps/500Kbps respectively.
* A single drop is limited to 6m.
* Each node on the network will have its own address between 0 and 63.

If a PLC-5 was to be connected to Devicenet a scanner card would need to be placed in the rack. The ladder logic in Figure 28.8 would communicate with the sensors through a scanner card in slot 3. The read and write blocks would read and write the Devicenet input values to integer memory from N7:40 to N7:59.

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