Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 92)

Publication AG-UM008C-EN-P - February 2005
3-24 Configuring MicroLogix 1100/1200/1500 Controllers
Duplicate Packet Detect Duplicate Detect lets the controller detect if it has received a message that is a
duplicate of its most recent message from the master station. If you choose duplicate
detect, the processor will acknowledge (ACK) the message but will not act on it since it
has already performed the message’s task when it received the command from the first
message.
If you want to detect duplicate packets and discard them, check this parameter. If you
want to accept duplicate packets and execute them, leave this parameter unchecked.
Poll Timeout The timer keeps track of how often the station is polled. If the station has a message to
send, it starts a timer.
If the poll timeout expires before the message timeout, which you specify in the MSG
control block, the MSG error bit is set and the message is removed from the transmit
queue.
If the message timeout, which you specify in the MSG control block, expires before the
poll timeout expires, the MSG error bit and MSG timeout bit are set.
The poll timeout can be disabled by entering a zero. See page 3-25 for
recommendations to minimize this value.
RTS Off Delay Defines the amount of time, in 20 millisecond increments, that elapses between the
end of the message transmission and the de-assertion of the RTS signal. This time
delay is a buffer to make sure that the modem has transmitted the message, but should
normally be left at zero. See page 3-11 for further guidelines for setting this parameter.
RTS Send Delay Defines the amount of time, in 20 millisecond increments, that elapses between the
assertion of the RTS signal and the beginning of the message transmission. This time
allows the modem to prepare to transmit the message. The Clear-to-Send (CTS) signal
must be high for transmission to occur.See page 3-11 for further guidelines for setting
this parameter.
Message Retries Defines the number of times a slave station resends its message to the master station
before the slave station declares the message undeliverable.
Pre-Transmit Delay 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.
EOT Suppression 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.
Table 3.5 Configuring a MicroLogix 1100/1200/1500 controller as a Slave Station
Parameter Selections