ProSoft Technology 5201-MNET-101S - Manual (Page 76)

Reference IEC-101 Slave ♦ ProLinx Communication Gateway
Protocol Manual IEC 60870-5-101 v3 Slave (Firmware version 3.xx)
Page 76 of 159 ProSoft Technology, Inc.
August 6, 2010
This example shows that the gateway sends all 40 measured scaled points in
one single message, if the message is not greater than 252 bytes. However,
some Master devices may not support messages containing this number of
bytes. If the Master for a given application supports only 100 bytes, the following
communication procedure would occur:
As shown in the previous diagram, the gateway sends out three (3) messages
(15 points, 15 points, and 10 points) instead of sending the whole 40 points in
one single message.
Note: This example shows the case where IOA Length = 3 bytes, COT Length = 2 bytes and
CASDU Length = 2 bytes.
Important: If the database parser gets a point index that is not valid, the whole database is set as
invalid and no points are reported. Because the index 0 is not valid (the protocol does not support
this index value), the driver considers it invalid. For example, if you set the size of the ASDU to 1
and you set a value of 1000 for a point index, this is also invalid as the indexes can only go from 1
to 255.