C:\BACNET\bin>bacwp --help
Usage: bacwp device-instance object-type object-instance property priority index tag value [tag value...]

device-instance:
BACnet Device Object Instance number that you are trying to communicate to.
This number will be used to try and bind with the device using Who-Is and I-Am services.
For example, if you were writing to Device Object 123, the device-instance would be 123.

object-type:
The object type is the integer value of the object that you are writing to.
For example if you were writing to Analog Output 2, the object-type would be 1.

object-instance:
This is the object instance number of the object that you are writing to.
For example, if you were writing to Analog Output 2, the object-instance would be 2.

property:
The property is an integer value of the property you are writing to.
For example, if you were writing to the Present Value property, you would use 85 as the property.

priority:
This parameter is used for setting the priority of the write. If Priority 0 is given, no priority is sent.
The BACnet standard states that the value is written at the lowest priority (16) if the object property supports priorities when no priority is sent.

index: This integer parameter is the index number of an array.  If the property is an array, individual elements can be written to if supported.  If this parameter is -1, the index is ignored.

tag: Tag is the integer value of the data type of the value that you are writing.  For example, if you were writing a REAL value, you would use a tag of 4. Context tags are created using two tags in a row.  The context tag is preceded by a C.  Ctag tag. C2 4 creates a context 2 tagged REAL.

value: The value is an ASCII representation of some type of data that you are writing.  It is encoded using the tag information provided.  For example, if you were writing a REAL value of 100.0, you would use 100.0 as the value.

Here is a brief overview of BACnet property and tags:
Certain properties are expected to be written with certain
application tags, so you probably need to know which ones to use
with each property of each object.  It is almost safe to say that
given a property and an object and a table, the tag could be looked
up automatically.  There may be a few exceptions to this, such as
the Any property type in the schedule object and the Present Value
accepting REAL, BOOLEAN, NULL, etc.  Perhaps it would be simpler for
the demo to use this kind of table - but I also wanted to be able
to do negative testing by passing the wrong tag and have the server
return a reject message.

Example:
If you want send a value of 100 to the Present-Value in
Analog Output 0 of Device 123 at priority 16, send the following command:
bacwp 123 1 0 85 16 -1 4 100
To send a relinquish command to the same object:
bacwp 123 1 0 85 16 -1 0 0
