ProSoft Technology MVI69-DNPSNET - Manual (Page 107)

Reference MVI69-DNPSNET ♦ CompactLogix or MicroLogix Platform
Distributed Network Protocol Interface Module
ProSoft Technology, Inc. Page 107 of 119
November 3, 2008
OBJECT REQUEST RESPONSE
Obj Var Description Func
Codes Qual
Codes
(hex) Func
Codes Qual
Codes
(hex) Data
Size
(bits) NOTES
20 Slave supports the Enable
Unsolicited Function
21 Slave supports the Disable
Unsolicited Function
23 Slave supports the Delay
Measurement & Time
Synchronization Function and
will return Obj 52, Var 2, Qual
7, Cnt 1
24 Slave supports use of this new
time synchronization function.
Used with Obj 52, Var 3.
5.9 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
The number of events that can be defined in the system is limited to 400. The
event buffer will overflow in systems which are very dynamic unless one of the
following conditions exist:
ƒ The master frequently polls the slave device for events to keep the buffer
empty.
OR
ƒ The slave is configured to send unsolicited messages to the master station.
This method requires full-duplex operation of the network because the slave
may be sending a message during a request from the master station.