MVI71-DNPSNET
♦
PLC Platform
Reference
Distributed Network Protocol Interface Module
Page 88 of 100
ProSoft Technology, Inc.
September 22, 2008
After the successful initialization of the module, the program will start the normal
data transfer between the module and the PLC processor. For the side-connect
interface, the module will interact directly with the user data files. For the block-
transfer interface, the program will send a BTR block first and then wait for a
BTW block to receive data from the PLC. This alternating sequence of read and
write will continue as long as the program is running. The program will update the
DNP memory areas in the module with the new data in the BTW and generate
events for digital and analog input status changes.
If the module is configured for unsolicited messaging, the module will
immediately send an unsolicited response once the remote master connects to
the module, informing the master of a module restart. The module will not log
events or process any data read operations from the master until the master
clears the restart IIN data bit. The master must also synchronize the time with the
module before events will be generated if the module is so configured. The
master is also responsible for enabling the unsolicited message facility in the
module by sending the Enable Unsolicited Messaging command to the module.
If the module is not configured for unsolicited messaging, the DNP master must
clear the restart IIN bit before the module will start logging events. The master
must also synchronize the time with the module before events will be generated if
the module is so configured.
Additionally, the program will listen on Port 1 for requests. This is the debug port
for the module and transfers module information to an attached terminal. Refer to
the
Diagnostics and Troubleshooting
section for a complete discussion on the
use of this important feature.
5.10 Event Size Computation
The minimum event buffer size required to avoid overflow can be computed as
follows:
((number of static points)*(rate per second scan of change function)) /(rate
per second of master event data poll)
For example: 51 binary input points are scanned 2 times each second and polled
by the master station about every 5 seconds. The minimum number of binary
input events is:
(51 * 2)/.02 = 510 events
This computation assumes the unlikely event that all data points will change in
consecutive calls to the scan of change function. If an event buffer overflow
condition occurs, the internal indication bit, BUFFER OVERFLOW, will be set. If
the system you are working with is fairly stable, the following equation can be
used to compute the event buffer size:
(number of points that change per change function * rate per second of scan of
change function) * (number of seconds between master event data poll)
For example: 1000 binary input points are scanned 2 times each second and
polled by the master station about every 5 seconds. Only about 5 points change
state every scan of the change function call.
(5 * 2) * 5 = 50 events required
Содержание InRax MVI71-DNPSNET
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