Question:
I'm having trouble with the wake up detection mechanism on the MAX14821 chip. According to your data sheet the chip should be able to detect a valid wake-up pulse on the C/Q line and then set the WU\ line low, but that doesn't seem to happen. Are there any other requirements for the automated detection?
Answer
The TXEN line has to be held HIGH for the /WU line being able to go LOW when a wake-up pulse is occurring on the C/Q line.
The device detects an IO-Link wake-up condition on the C/Q line in push-pull, high-side (PNP), or low-side (NPN) operation modes. A wake-up condition is detected when the C/Q output is shorted for 80us (typ). WU pulses low for 190us (typ) when the device detects a wake-up pulse on C/Q. Set the WuIntEn bit in the Mode register to set the WuInt bit in the Status register and generate an interrupt on IRQ when a wake-up pulse is detected. WuInt is set and IRQ asserts immediately after C/Q is released when WuIntEn = 1.