GE 90-30 PLC, User Manual

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2-6 Series 90™-30 PLC LONWORKS® Bus Interface Module User's Manual – June 1997 GFK-1322A
2
Sweep Operation
The data flow for information that is sent from the L
ON
W
ORKS
network to the PLC is handled
separately from the flow of data from the PLC to the L
ON
W
ORKS
network.
Input data: When an input network variable is updated, the data associated with the network
variable is copied into the proper location in a PLC input buffer. The Store Inputs routine is then
called to update the data in the PLC at the next scan time.
Output data: When the API callback notifies the LBIM that an output scan has arrived, the data
is copied into a holding buffer. This buffer is then scheduled to be checked against the current
value of each output network variable. If the data is different, the network variable is updated over
the L
ON
W
ORKS
network if the Min Send Time for the network variable has expired (only if Min
Send Time was configured). This prevents overloading the network with frequently changing
data.
If a network variable is configured to be a SNVT_lev_disc or a SNVT_switch and is mapped into
the %I or %Q reference area, the data is converted to a bit. This conversion occurs when the data
is moved to or from the PLC buffer.
The total sweep time depends on the amount of reference memory used by the LBIM. This is a
maximum of 1K words input and 1K words output, and is set when the LBIM’s Network Interface
is configured.
The I/O response times depend on the following factors:
•
number and size of network variables for which the LBIM is configured
•
rate at which network variables are updated
•
number of network variables that are bound
•
service type (ACKD, UNACKD) of each network variable
•
network bandwidth
•
network traffic
•
whether network variables are input or output network variables