Filter
Top Products
5-4 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual
–
May 2002 GFK-1541B
5
Asynchronous Operation of EGD
The production and consumption of EGD is asynchronous. The period timers for the producer
and consumer are independent of each other. In addition, the initiation of the production and
consumption of EGD can occur at different times.
The figure below illustrates the asynchronous aspect of EGD in all Ethernet Interfaces except the
Series 90-30 CPU374. In the Series 90-30 CPU374, there is no consumer period. When data is
received, it is made available to the application on the next PLC sweep.
•
Producer period timer starts.
•
Exchange Status word is set to 0.
•
First exchange data sample is sent
onto the network.
PLC Producin
g
EGD
PLC Consumin
g
EGD
EGD Production Is Initiated
EGD Consumption is Initiated
•
Consumer period timer starts. *
•
Exchange Status word is set to 0.
EGD Consumption Repeats
•
Consumer period timer expires and
is restarted. *
•
Exchange data sample received
from the network is updated in
consumer PLC memory.
•
Exchange Status word is set to 1
(or 3 if SNTP timestamping is used).
EGD Production Repeats
•
Producer period timer expires and is
restarted.
•
Exchange data sample is sent onto
the network.
•
Exchange Status Word set to 1.
•
Consumer period timer expires and
is restarted. *
•
Exchange data sample received
from the network is updated in
consumer PLC memory.
•
Exchange Status word is set to 1
(or 3 if SNTP timestamping is used).
•
Producer period timer expires and is
restarted.
•
Exchange data sample is sent onto
the network.
•
Exchange Status Word set to 1.
Producer
period
Producer
period
Consumer
period *
Consumer
period *
via LAN
* Does not apply to CPU374
The figure presents a simplified overview of EGD. There are other timing issues regarding data
transferred from the Ethernet Interface to the PLC CPU that could be an issue depending on your
application. See the topic, “Configuration Planning,” for more information.