Echelon OpenLDV - Manual (Page 71)

OpenLDV Programmer’s Guide 63
• NetVarHdr — for sending and receiving network variables that are
processed by the network interface
ExpMsgHdr
7 6 5 4 3 2 1 0
msgtype service type auth tag
Priority Path compl code
addr
mode alt path
pool resp
length
msgtype
The msgtype field is set to 0 for the ExpMsgHdr.
service type
The service type field contains one of the following values, depending on
which LonTalk protocol messaging service is to be used for delivery of the
message:
• ACKD (0) for the acknowledged messaging service
• UNACKD_RPT (1) for the repeated messaged service
• UNACKD (2) for the unacknowledged messaging service
• REQUEST (3) for the request/response messaging service
auth
The auth field is set to 1 for a downlink message (sent to a network interface)
if the receiver must authenticate the message using LonTalk authentication.
A network interfaces might require authentication for local network
management commands.
It is set to 1 for an uplink message (read from a network interface) if the
message has been authenticated by the network interface.
If authentication is not enabled on the network interface, this field should be
set to 0.
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 (those that use the full 3-layer address),
you can segt the tag 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 (one that specifies an entry in the address table), 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.