We are power profiling our new LoRa Sensor based on RAK4270 and have found the resulting problem
Put RAK4270 to Sleep
Put HOST CPU to Sleep. All I/O Lines Tristate / Disabled. TXD to RAK4270 low (not driven)
The HOST CPU wakes up and at this point the TXD goes high
This causes the RAK4270 to exit sleep and therefore waste power.
I have tried a large pullup (150K) on the RXD Line and this causes the RAK4270 to draw more power in sleep mode.
I cannot find documentation stating that the RAK wakes up on a rising edge of the RXD line !