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Curtis 3140 Manual – Nov. 2017
STANDARD MESSAGE IDENTIFIERS
The Model 3140 will produce—and respond to—the standard message types with the following CANopen
identifiers.
The 11-bit identification field is a fixed part of the CANopen specification called the Communication OBject
IDentification (COB-ID). This field is used for arbitration on the bus. The COB-ID with the lowest value gets
priority and wins arbitration. Consequently, NMT messages have the highest priority of the standard message
types, and the heartbeat has the lowest priority.
The standard organization of the COB-ID puts the message type in the upper four bits, and the Node ID in the
bottom seven bits:
11
Message Type
NMT MESSAGES
NMT (Network Management Transmission) messages are the highest priority message available. The NMT
message puts the Model 3140 into one of the four defined states. These messages have 1 byte of data sent by the
master; the slave does not respond with any data to an NMT. The Model 3140 state value is transmitted with
each heartbeat message.
The NMT message identifier consists of the standard message type (NMT)
in the top four bits; the bottom seven bits must be set to zero.
pg. 4
Message Type
NMT
PDO-MISO
PDO-MOSI
SDO-MISO
SDO-MOSI
HEARTBEAT
10
9
8
7
Value
0x00
0x04
0x05
0x7F
Message Identifier
0000 – 0x00
0011 – 0x03
0100 – 0x04
1011 – 0x0B
1100 – 0x0C
1110 – 0x0E
6
5
4
3
Node ID
State
Initialization (or "boot-up")
Stopped
Operational
Pre-Operational
2
1
3 — CANopen COMMUNICATIONS
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