Echelon OpenLDV User Manual download pdf (Page 82)

74 Sending and Receiving Messages with the OpenLDV API

UnprocessedNV

7 6 5 4 3 2 1 0

1 dir

selector

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

1 2 ... 77 78 79 80 81 82 83 84 85 86 87 ... 193 194

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Echelon OpenLDV User Manual Page 82