Allen-Bradley controllogix 1756-L63, User Manual

Page: 346 / 435

Publication 1756-UM001E-EN-P - August 2002
20-30 Communicate Over a Remote I/O Network
Stagger the Messages
As you add messages to your project, you may have to coordinate the
execution of the messages. To avoid errors and assure that each
message is processed, follow these rules:
If the number of messages in your application exceeds rules 1 and 2,
then stagger the execution of your messages. Here are some options:
•
Send each message in sequence
•
Send the messages in groups that are within the limits of rules 1
and 2
•
Program a message to communicate with multiple devices. Refer
to Read or Write Data To or From Multiple Block Transfer
Modules on page 20-15
Rule 1: Enable no more than 16 messages at one time (including block transfers).
Rule 2: Enable no more than 10 of the following types of messages at one time:
•
CIP data table reads or writes that are not cached
•
CIP generic
•
PLC2, PLC3, PLC5, or SLC (all types)
•
block transfer reads or writes that are not cached