Echelon OpenLDV - Manual (Page 82)

74 Sending and Receiving Messages with the OpenLDV API
UnprocessedNV
7 6 5 4 3 2 1 0
1 dir NV selector hi
NV selector lo
NV data
Depending on the context, this form of the data field is used for network-variable
update messages, poll messages, poll responses, or completion events. A
network-variable update message or a poll response contains 1-31 bytes of
network-variable data. A network-variable poll request message or a completion
event contains no data, only the selector in the first two bytes.
Set the direction bit to 1 for polling an output network variable, and 0 for
updating or polling an input network variable.
An OpenLDV application that sends a downlink network-variable message must
retrieve the appropriate network variable selector from its network variable
configuration table or alias table. Similarly, when an uplink network-variable
message arrives, the OpenLDV application looks up the network variable selector
from the message in its network variable configuration table or alias table to
determine which network variable was addressed.
For more information about network variable configuration, messages, and alias
tables, see the ISO/IEC 14908-1 protocol specification.
ExplicitMsg
7 6 5 4 3 2 1 0
0 Message code
Message code
Depending on the context, this form of the data field is used for downlink
messages, uplink messages, or completion events. A downlink or uplink message
contains 0-228 bytes of data. A completion event contains only the message code
and the first byte of the data. Message codes for non-response messages are
allocated as listed in Table 31.
Table 31. Message Codes for Application Messages
Message Type Message Codes (Hex)
User application message 00 .. 2F
Standard application message 30 .. 3E
Responder offline 3F
Foreign message 40 .. 4E