Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 93)

Publication AG-UM008C-EN-P - February 2005
Configuring MicroLogix 1100/1200/1500 Controllers 3-25
Configuring Poll Timeout The Poll Timeout is only used when the DF1 half-duplex slave is
initiating MSG instructions in ladder logic. This implies that the Master
is most likely configured for Standard Polling Mode. The minimum
Poll Timeout value is dependent on the maximum Master poll scan
rate. Since the Master’s polling and the Slave’s triggering of a MSG
instruction are asynchronous events, it is possible that in the instant
just after the slave was polled, the MSG instruction gets triggered. This
means the MSG instruction will remain queued-up for transmission
until the Master has polled every other slave first. Therefore, the
minimum Slave channel 0 Poll Timeout value is equal to the
maximum Master poll scan rate rounded up to the next 20 ms
increment.
DF1 Half-Duplex Slave Channel Status
Channel Status data is stored in the Communication Status Function
file. Table 3.6 on page 3-25 explains information regarding the
diagnostic counter data displayed.
Minimum Channel 0 Poll Timeout = Maximum Master Scann Poll Rate
1. Double-click on the Channel
Status Icon Located beneath
the Configuration icon to bring
up the Channel Status screen.
Table 3.6 Understanding the DF1 Half-Duplex Slave Status Screen Fields
Status Field Communication Status
Function File Location
(2)
Definition
Messages Sent CSx:10 The total number of DF1 messages sent by the processor (including
message retries)
Messages Received CSx:11 The number of messages received with no errors
Polls Received CSx:15 The number of master poll packets received by the processor
Received NAK CSx:14 The number of NAKs received by the processor
Lack of Memory CSx:17 The number of times the processor could not receive a message because
it did not have available memory