Let’s explore the Control Bit Vector (CBV) and the Active Wakeup Bit (Bit 4) in the context of CAN Network Management (NM).

Active Wakeup Bit in CAN NM’s Control Bit Vector

In CAN NM, the Control Bit Vector (CBV) is a crucial part of the NM message, and it includes an Active Wakeup Bit (Bit 4) that indicates how a wake-up was initiated:

• Bit 4 = 0: The node has not actively initiated a network wake-up, meaning it was a passive wake-up.
• Bit 4 = 1: The node has actively initiated a network wake-up, making it an active wake-up.

Practical Differences: Passive vs. Active Wake-Up in CAN NM

1. Active Wake-Up (Bit 4 = 1):
   • When Bit 4 is set to 1, it tells other nodes on the CAN network that the transmitting node has actively woken up the network.
   • This often occurs when a node detects an internal event that requires network communication, like a user interaction or sensor alert.
2. Passive Wake-Up (Bit 4 = 0):
   • If Bit 4 is set to 0, the wake-up was passive; the node didn’t initiate it but is acknowledging network activity.
   • This passive wake-up can occur when a node simply detects CAN bus activity (e.g., another ECU is communicating) and joins the network without explicitly requesting it.

Example of Control Bit Vector in Action

Imagine a scenario with two ECUs, ECU A and ECU B, on a CAN network:

• Active Wake-Up: ECU A detects an important event, like an ignition key turn, and transmits an NM message with Bit 4 set to 1. This signals to other ECUs, including ECU B, that ECU A actively initiated the network wake-up.
• Passive Wake-Up: Later, ECU B receives CAN bus activity without needing to wake up other nodes. It sets Bit 4 to 0 in its NM message, informing others that it hasn’t actively requested the wake-up but is simply joining the ongoing communication.

Summary

The Active Wakeup Bit in CAN NM’s CBV provides a direct, clear indication to other ECUs about whether a wake-up was initiated actively by a node or was merely a passive response to existing network traffic. This distinction optimizes power management and communication clarity within the CAN network.

Reference

Details	Link
Specification of CAN Network Management	https://www.autosar.org/fileadmin/standards/R21-11/CP/AUTOSAR_SWS_CANNetworkManagement.pdf

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