The MAX22515 wake-up detection scheme is a little more complicated than the MAX22513. First of all, there are two modes for the MAX22515: I2C mode, and pin mode.
In I2C mode:
When TXEN = high, the MAX22515 detects a wake-up condition by current pulse only. In PNP mode and NPN mode, when the TX = high or low, respectively, there is no current required to pull the pin high or low. This means there is no current pulse, and a wake-up event is not detected.
In this mode, however, a wake-up is also detected when TXEN = 0. This allows one to use a sort of pseudo-PNP and NPN mode, and still detect a wake-up pulse. In this case, one would need to configure the device as follows to detect a wake-up in a PNP state with C/Q in high impedance:
CQ_EN = 1 (driver is enabled)
CQ_PP = 1 (push-pull mode enabled)
TX = 0 (high side enabled, simulates PNP)
TXEN = 0 (C/Q is high impedance)
In this configuration, C/Q emulates the PNP mode in a high impedance state, and a wake-up can be detected when C/Q is pulsed high to low. Similarly, if TX = VL and TXEN = 0 (emulated NPN mode) and a low-to-high pulse is received on C/Q, the device will assert the WU pin.
Pin Mode:
In this mode, the device only detects a wake-up event when TXEN is high. This is more like a ‘typical’ wake-up detection scheme, but this mode does not allow one to set the C/Q configuration – C/Q is in PP mode only in pin mode.