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page 554

7

- application

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

- presentation

 

 

 

 

 

 

 

 

gateway

 

 

 

 

 

 

 

 

 

 

 

 

5

- session

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

- transport

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

- network

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2

- data link

 

 

 

 

 

router

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

- physical

 

bridge

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

31.7 BUS TYPES

Low level busses,

-RS-485

-Bitbus

-CAN bus

-Lonworks

-Arcnet

General open buses,

-ASI

-Devicenet

-Interbus-S

-Profibus

-Smart Distributed System (SDS)

-Seriplex

Specialty buses,

-Genius I/O

-Sensoplex

page 555

31.7.1 Devicenet

Devicenet is meant as a noise resistant, robust, shop floor network.

The main change that the user will notice is that a rack of a PLC can be broken up and CPU, I/O, etc. are now connected by Devicenet.

Devicenet is an open standard, so components can come from a variety of suppliers.

Based on the CANbus (Controller Area Network) protocol.

Some advantages,

-open system is not tied to a single vendor

-diagnosis of devices is possible

-wiring becomes easier (no long wire runs)

-complex devices are easy to connect

-possibility of using a PC based control package

-multiple controllers can share the net

Basic features

-up to 64 nodes on the network

-lengths of 500m/250m/100m for speeds of 125kbps/250kbps/500kbps respectively

-data packet size of 0-8 bytes

-power and signal in the same cable

-single bus cable

-addressing includes peer-to-peer, multicast, master/slave, polling or change of state

-devices can be added/removed while power is on

Devicenet is a layer 7 - application protocol (Note that CANbus is level 2)

A typical structure for Devicenet is shown below,

page 556

 

 

thin

 

 

thin

 

 

 

 

thick trunk line

 

 

trunk tap

 

 

trunk

 

 

 

 

 

 

 

 

power tap

 

 

line

 

 

 

 

line

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

terminator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

drop

 

 

 

 

 

flexIO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

line

 

 

 

 

 

 

PC

 

 

 

 

 

 

 

 

 

rack

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

tap

 

 

 

 

 

 

drop

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

line

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

smart

 

 

 

flexIO

 

 

power

 

 

 

 

 

 

 

 

rack

 

 

supply

 

 

 

 

 

sensor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

terminator

• There are two types of wire used,

Thick trunk - carries up to 8A for power up to 500m Thin trunk - up to 3A for power up to 100m

power (24Vdc)

data

drain/shield

Power supplies are directly connected to the cable to supply power.

The drop lengths are limited

-total length/speed 156m/78m/39m are 125Kbps/250Kbps/500Kbps respectively

-a single drop is limited to 6m

The wiring can come in a form of end/connectors,

-bare wires

-unsealed screw connector

-sealed mini connector

-sealed micro connector

-vampire taps

page 557

• Devices may have a red/green status light for the network status.

Devicenet used the CANbus indentifier to specify, message types (5 bits)

node number (6 bits) up to 64 nodes on the net

On a PLC-5 rack you would need a devicenet interface and could use the instructions below.

N7:0/EN

MSG

 

 

(EN)

N7:0/EN

MSG

 

 

(EN)

 

 

 

 

 

 

 

 

 

 

Send/Rec Message

 

 

 

 

Send/Rec Message

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(DN)

 

(DN)

 

 

 

Control Block N7:0

 

(ER)

 

 

 

Control Block N7:0

 

(ER)

 

 

 

 

 

 

 

 

 

 

 

 

 

Read/Write

Write

 

 

Read/Write

Read

 

 

 

 

 

Data Table

N7:20

 

 

Data Table

N7:40

 

 

Size

 

20

 

 

 

Size

20

 

 

 

Local/Remote

Remote

 

 

Local/Remote

Remote

 

 

Remote Station

??

 

 

 

Remote Station

??

 

 

 

Link ID

??

 

 

 

Link ID

??

 

 

 

Remote Link type

??

 

 

 

Remote Link type

??

 

 

 

Local Node Addr.

N/A

 

 

Local Node Addr.

N/A

 

 

Processor Type

????

 

 

 

Processor Type

????

 

 

 

Dest. Addr.

N7:40

 

 

Dest. Addr.

N7:20

 

Note:

• On a Softlogix PLC the I/O will be copied into blocks of integer memory. These blocks are selected by the user in the setup of the software. Here the inputs are copied into N9 integer memory, and the outputs are set by copying the N10 block of memory back to the outputs.

N9:0

N10:23

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