Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Uživatelský manuál stáhnout pdf (Strana 229)

Data Link Layer

Appendix E

E-2

When a station gains control of the Data Highway to transmit messages, it

has become a master station. All other station interface modules assume a

slave mode. This enables these stations to receive and acknowledge

messages sent to them. Basically, a station has three states of operation:

Transmitting Messages

Polling to Determine which Station Gets Mastership Next

Receiving Messages and Polls

Thus, each Data Highway station can transmit and receive both messages

and polling sequences.

Figure E.1 shows the change of states at a Data Highway station.

Figure E.1

State

Transition at Master Station

11536

Received

Mastership

Polling

Sending

Received

Relinquished

Mastership

All Sent or Max. of 16 or

All High Priority Messages

Sent and Response to High

Priority Global Poll

Contention

Have

Messages to

Send and All

Stations Have

Been Polled

at Least Once

State

1 2 ... 224 225 226 227 228 229 230 231 232 233 234 235

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Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Uživatelský manuál Strana 229