BB2-7030 User Guide – Rev. 1.0
Page 50
Data from the local object may be manipulated before being written to the remote OID. The local
data is first multiplied by the scale factor. The offset is then added to it. The data is then sent to
the remote SNMP agent. Enter the full OID to be written, the SNMP ASN data type to be written
(select from list), and the location (device). The names in the device list are defined in the
Devices page.
Important note about data type: SNMP does not have a universally accepted representation for
floating point. The most commonly used means of representing real data is scaled integers, and
this method is supported by BB2-7010. IEEE 754 is not recognized as an SNMP standard and is
not used. X.690 defines an encoding for real data, but it is inefficient and little used. A common
recommendation is to use ASCII string representation of floating point data, and this method is
supported by BB2-7010 (Octet String Num). Another known but application specific
implementation is the ASN OPAQUE FLOAT used in netsnmp applications. This method is also
supported by BB2-7010 but should be tested to confirm compatibility.
The repeat time may determine how often the remote OID will be written. If send on delta and
maximum quiet time are not checked above, clicking the "at least" button will establish a
periodic update time. If send on delta is used and you wish to limit the network traffic in the
event changes are frequent, click the "no more than" button and enter the minumum time that
should elapse before another write to the remote device.
Delete will remove the rule number shown in the "Map #" box. Insert will insert a new rule
before the rule number shown, and is used for placing rules between existing rules. It is not
necessary to use Insert to add rules to the bottom of the list or to define any rule presently having
zero/none for a source object.
Selecting "none" for remote type effectively deletes the rule even though it will still appear in the
list until deleted. Unused rules at the end of the list will always show none as the type. If you
wish to prevent these from being displayed, reduce the number of rules enabled.
Initial COV increment and period will only apply if a BACnet client subscribes to COV
notification from the BACnet object assigned to this Modbus map. These properties may be
overwritten by the BACnet client(s) at any time. The values shown here are initial values, not
necessarily the current values. (Note: COV increment only applies to Analog objects, all changes
are reported for Binary or Multistate objects.)
Units default to no_units, but you may select any of the available BACnetEngineeringUnits
values. This value will simply be read by the BACnet client when the units property is requested
from the object this OID maps to. The units have no bearing on calculations performed. You
must select appropriate scale and offset values to make any required translation between SNMP
units and BACnet units. Units are only valid for Analog objects.
Initial Relinquish Default may be set here, but may be overwritten by the BACnet client at any
time. This window reflects the initial value, not the current value. (Note: Relinquish Default only
applies to commandable Output objects, and does not apply to Input or Value objects.)
