The TCAN1044A(V)-Q1 supports a remote wake-up request that is used to indicate to the host controller that the bus is active and the node should return to normal operation.
The device uses the multiple filtered dominant wake-up pattern (WUP) from the ISO 11898-2:2016 standard to qualify bus activity. Once a valid WUP has been received, the wake request is indicated to the controller by a falling edge and low period corresponding to a filtered dominant on the RXD output of the TCAN1044A(V)-Q1.
The WUP consists of a filtered dominant pulse, followed by a filtered recessive pulse, and finally by a second filtered dominant pulse. The first filtered dominant initiates the WUP, and the bus monitor then waits on a filtered recessive; other bus traffic does not reset the bus monitor. Once a filtered recessive is received the bus monitor is waiting for a filtered dominant and again, other bus traffic does not reset the bus monitor. Immediately upon reception of the second filtered dominant the bus monitor recognizes the WUP and drives the RXD output low every time an additional filtered dominant signal is received from the bus.
For a dominant or recessive to be considered filtered, the bus must be in that state for more than the tWK_FILTER time. Due to variability in tWK_FILTER the following scenarios are applicable. Bus state times less than tWK_FILTER(MIN) are never detected as part of a WUP and thus no wake request is generated. Bus state times between tWK_FILTER(MIN) and tWK_FILTER(MAX) may be detected as part of a WUP and a wake-up request may be generated. Bus state times greater than tWK_FILTER(MAX) are always detected as part of a WUP, and thus a wake request is always generated. See Figure 9-5 for the timing diagram of the wake-up pattern.
The pattern and tWK_FILTER time used for the WUP prevents noise and bus stuck dominant faults from causing false wake-up requests while allowing any valid message to initiate a wake-up request.
The ISO 11898-2:2016 standard has defined times for a short and long wake-up filter time. The tWK_FILTER timing for the device has been picked to be within the minimum and maximum values of both filter ranges. This timing has been chosen such that a single bit time at 500 kbps, or two back-to-back bit times at 1 Mbps triggers the filter in either bus state. Any CAN frame at 500 kbps or less would contain a valid WUP.
For an additional layer of robustness and to prevent false wake-ups, the device implements a wake-up timeout feature. For a remote wake-up event to successfully occur, the entire WUP must be received within the timeout value t ≤ tWK_TIMEOUT. If not, the internal logic is reset and the transceiver remains in its current state without waking up. The full pattern must then be transmitted again, conforming to the constraints mentioned in this section. See Figure 9-5 for the timing diagram of the wake-up pattern with wake timeout feature.