Rockwell-automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM Manual de usuario descargar pdf (Pagina 27)

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101

Publication AG-UM008C-EN-P - February 2005

Designing Communication 1-9

When the master station is configured for standard-communication

mode, you do not need to program any master-station message

instructions to communicate with slave stations. Communication with

slave stations occurs by the master station sending polling packets to

slave stations. You only need message instructions when you want the

master station to write data to or read data from a location within a

slave station’s data table.

Figure 1.2 Standard Communication Mode

To help you understand See

standard-communication mode Figure 1.2

how a master station requests data Figure 1.3

41181

• Check for and send

outgoing MSG

• Select next station

to poll

timeout received and

station inactive

timeout received and

station active and

tries > ‘DF1 message

retries’ make

station inactive

EOT received indicating no MSG to

send make station active

(if inactive)

MSG received and single

poll mode forward data

to or return data from

data table

• Send poll

• Start ACK timeout

• Wait for EOT or

MSG (or timeout)

MSG received and

multiple mode

forward data to or

return data from

data table

timeout received and

station active and tries

< or = ‘DF1 message

retries’

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Rockwell-automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM Manual de usuario Pagina 27

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