Bradley Smoker PLC-5 user manual Message Destination, 14Communicating with Devices on a DH+ Link

9-14Communicating with Devices on a DH+ Link

The number of messages a station has to send also affects throughput time. For example, if a station has three messages queued and a fourth is enabled, the fourth message may have to wait until the previous three are processed.

Message Destination

Throughput times vary depending on whether a receiving station can process the message and generate a reply before it receives the token. The figure below assumes that station 1 wants to send a message to

station 4.

1.Station 1 has the token. Only the station that has the token can send a message. Station 1 sends the message to station 4.

Station 5

Station

1

Message

2.Now station 1 must pass the token on to the next next highest station number, which is station 2.

Station 2

Station 4

Station

1

Station

3.Station 2 has the token. Assume that station 2 has messages to send and holds the token for 30 ms. During this time, station 4 has processed the message from station 1 and has a reply queued up. When finished, station 2 passes the token on to the next highest station number, which is station 4.

Station

5

4. Station 4 can now reply to the message from station 1. This

Message

2

completes the message transaction.

Station 4

Publication 1785-UM012D-EN-P - July 2005