Configuring Channel 0 Poll Timeout - Allen-Bradley SLC 500 Series Reference Manual
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Table 13.22 Define these parameters when configuring a SLC 5/03, 5/04, or 5/05 processor as a slave station. (Continued)
Tab
Parameter
Default
Message
3
Retries
Pre-Transmit
0
Delay
EOT
Unchecked
Suppression
Selections
Defines the number of times a slave station resends its message to the master station before
the slave station declares the message undeliverable.
Defines the amount of time in 1 millisecond increments that elapses between when the
processor has a message to send and when it asserts the RTS signal (if handshaking is selected)
or begins transmitting (if no handshaking is selected).
If you want to minimize traffic on the network, you can choose to have the slave station not send
EOT packets to the master station. When EOT packets are suppressed, the master station
automatically assumes a slave station has no data to give if the slave station does not send a
message packet as a response to a poll. A disadvantage of suppressing EOTs is that the master
station cannot distinguish between an active station that has no data to transmit and an inactive
station. A possible application for suppressing EOTs is the following: conserving power with a
radio modem because the radio transmitter does not have to power-up to transmit a DLE EOT
packet (no data to give packet). To suppress EOTs, check this parameter. To have the processor
send EOTs, leave this parameter unchecked.
Configuring Channel 0 Poll Timeout
The Channel 0 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.
Minimum Channel 0 Poll Timeout = (maximum Master scan poll rate)
SLC Communication Channels
Publication 1747-RM001G-EN-P - November 2008
13-73
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