hi there,
1. can you explain why this contradicting statement is given , as bus forwarding for a unenumerated device does not make sense.
2. how is there a two wakeup as one signal is from the MCU is for bus activity and then the second signal is wakeup command that wakes the device ,so how is it two wake up command ,is it same like enumeration of device by the MCU that is given before ?
Hi,
Yes, Wake-Up 3 is essentially the propagation of Wake-Up 1, initiated by the MCU.
BRs, Tomas
the wake up 3 in the diagram is the propagation of the wake-up1 if i am not wrong ?
Hi,
I do apologize for the delay in getting back to you, some of my colleagues are already on Christmas vacation so I am unable to respond in time.
Let me try to clarify it a bit more.
IC1 Sends a Wake-Up Message to IC2:
Key point: This wake-up propagation mechanism is independent of normal bus forwarding, which is only enabled after enumeration. The wake-up message is treated as a special case.
- Once IC1 is active, it automatically generates a wake-up message (Wake-Up 2), specifically intended for IC2 (the next device in the daisy chain).
- This wake-up message is sent downstream even though IC1 is still unenumerated. The MC33774 has a built-in mechanism to forward wake-up messages even when the device itself does not yet forward general communication.
IC2 Detects Wake-Up Message from IC1:
- The wake-up message from IC1 is received by IC2. Upon receiving this message, IC2 transitions to Active mode.
- IC2 then automatically prepares to send its own wake-up message downstream.
Wake-Up Propagation Continues Downstream:
-Once IC2 is in Active mode, it sends a wake-up message to IC3.
- This process repeats for each device in the daisy chain until all devices are active.
In summary, wake-up propagation does not rely on general bus forwarding. Each device in the chain has a special mechanism to recognize and forward wake-up messages. The wake-up sequence ensures all devices transition to Active mode sequentially, even if they are unenumerated. After all devices are awake, the MCU can enumerate them and enable full bus forwarding for normal communication.
BRs, Tomas
hi Tomas ,
can you explain how the bit more as i am unable to understand how is the propagation of the second wakeup happening s as it will be a bus signal to IC2 and does not take it to active state and in IC2 still bus forward is not enabled , how will it propagate downstream to wake other devices in the chain?
Thank you
Shreyas Bhat
Hi,
The apparent contradiction arises because the datasheet refers to two separate states: unenumerated devices and bus forwarding enabled. Here is the key difference:
• Unenumerated Device: Before assigning a unique daisy chain address (DADD), the MC33774 does not forward messages to the next device. This ensures communication is limited to the first device in the chain during the initial setup or wake-up phase.
• Bus Forwarding Enabled: After an unenumerated device wakes up, it enables communication (including wake-up messages) to propagate down the daisy chain. This is why the statement mentions that the unenumerated MC33774 automatically sends wake-up messages to the next device.
In essence, the datasheet clarifies that the wakeup propagation (not full bus communication) is temporarily allowed during the wake-up process, even for unenumerated devices. The "contradiction" is a misinterpretation because the bus forwarding here refers specifically to wake-up messages, not general communication.
The two wake-up signals described in the diagram refer to the sequence of events for waking up a daisy-chained system:
• Wake-Up 1 (Bus Activity): The MCU sends a general signal or bus activity. This activity alerts the first MC33774 (IC1) to transition to Active mode.
• Wake-Up 2 (Wake-Up Command): Once IC1 is active, it sends a specific wake-up message to IC2 (the next device in the chain) as part of the daisy-chaining mechanism. This second wake-up signal propagates downstream to wake up other devices.
This is not the same as the enumeration process (where unique DADD addresses are assigned by the MCU). Instead, it is a preliminary step to ensure all devices in the chain transition from Sleep or Deep Sleep mode to Active mode.
BRs, Tomas