Echelon OpenLDV - Manual (Page 73)

OpenLDV Programmer’s Guide 65
alternate path
If the alternate path bit is set, the message is delivered on the path specified
in the path bit, otherwise it is delivered on the default path.
pool
Set the pool bit to 0 for a downlink message.
response
Set the response bit to 1 for a downlink response message, and 0 otherwise. If
it is set for an uplink message, the message is a response to a previously sent
request.
length
The length field in the message header is distinct from the length field in the
application layer header. The length field the message header indicates the
number of bytes for the message data.
NetVarHdr
7 6 5 4 3 2 1 0
msgtype poll resvd tag
Priority Path compl code
addr
mode trnarnd
pool resp
length
msgtype
The msgtype field is set to 1 for the NetVarHdr.
poll
The poll field is set to 1 for a network variable poll message. For other
network variable messages, it is set to 0 (zero).
reserved
The NetVarHdr includes two bits that are reserved for future use. Set this
field to 0 for downlink messages.
tag
The OpenLDV application uses the tag field for a downlink message (sent to a
network interface) to correlate returned responses and completion events.
For explicitly addressed messages, the tag can be set to any value in the
range 0-14, and the same value is returned with the corresponding responses
and completion events. In this case, the tag is also known as the reference
ID. For a downlink implicitly addressed message, the tag field is used as an
index into the address table of the Smart Transceiver or Neuron Chip in the
network interface to indicate the destination address of the message. For
more information about the address table, see the ISO/IEC 14908-1 protocol
specification.
For an uplink message (read from a network interface), the tag field indicates
the index into the receive transaction database for acknowledged, repeated