Part Number: MSP430FR2676
I designed 3 capacitive keypads:
- a 7-key ( self-capacitance );
- a 6-key ( self-capacitance );
- a 40-key ( mutual-capacitance );
They work in low power mode LPM3 with a constant active mode scan rate as defined in the Captivate Design Center. All these keypads work fine.
Now my customer asked if it is possible to lower the power consumption. So I selected in every design the sensor with the 7 / 6 / 40 keys as "Wake On Proximity Sensor" en enabled "Force LPM4 in Wake-on-Prox Mode".
For the 6-key version this works as expected: the current consumption is lower and when I touch any of the keys, the keypad reacts. See the configuration of the connections in this picture:
For the 7-key version I see a problem: when the key connected to controller port CAP3.1 is the first pressed key, the keypad does not react. Only when I touch one of the other 6 keys, the keypad wakes up. After it is awake, the key connected to controller port CAP3.1 also works. See the configuration of the connections in this picture:
For the 40-key version, the problem is worse: only the key connected between CAP3.0 and CAP0.0 will wake-up the keypad. After that key is touched, all keys work again if pressed within the Inactivity Timeout. See the configuration of the connections in this picture:
My questions:
- Is this normal behaviour?
- If yes, is there documentation which describes what controller ports can be used for wake-up and which not?
- Is there a workaround so that the keypads wake up, no matter what key is touched first?
Thanks for all suggestions.
