Message identifier bits
10 9 8 7 6 5 4 3 2 1 0
CANopen Function code (0–15) CANopen node ID (1–127, 0 reserved)
MicroMessaging Unused (8-bit only) Function code (0–7) MicroMessaging node ID (1–31, 0 reserved)

Table 1—The message identifier used in CANopen (11 bits) and MicroMessaging (e.g., 8 bits) is divided into a node ID field, which allows addressing a specific node, and a function code field, which specifies the contents of the message (e.g., one code is used for service requests sent to the node).