Bradley Smoker PLC-5 user manual Internal Processing Time

Communicating with Devices on a DH+ Link 9-15

In the following figure, station 4 has had time to process the message and generate a reply. However, in , station 2 does not have sufficient time to process a MSG reply.

1.In this figure, we assume that station 1 wants to send the identical message as shown in Figure but to station 2. Station 1 has the token. Station 1 sends the message to station 2 and then passes the token on to station 2.

Station

1

Message

2.Now station 2 has the token but has not had time to generate a reply to station 1. So station 2 sends any other messages it has queued and then passes the token on to station 4.

Station 5

Station 4

Station 2

3. Stations 4, 5, and 1 all receive the	Station
token in order and send any	5
messages they have queued.

4.The token then returns to station 2, which then sends its reply to station 1.

Station

1

Message

Station 2

In this example, it took an extra token pass around the network to complete the message transaction even though the message was identical to the one shown in Figure 10.2.

.

Station 4

Internal Processing Time

Internal processing time depends on how busy a given controller on the network is when sending or receiving a message.

For example, controller A has just received a READ request from controller B on the network. If controller A already has three messages of its own to send, the reply to the READ request from controller B will have to wait until the station completes the processing of the messages queued ahead of it.

Publication 1785-UM012D-EN-P - July 2005