How to set unused pins of MC9S12X in STOP mode to reduce power consumption

[wangbengang]

How to set unused pins of MC9S12X in STOP mode to reduce power consumption ！

[lama · Accepted solution]

Hi,

When the MCU enters full stp mode all the clocks are stoped and the CMOS device is in the static mode. None of the pins changes its status. If the output pins does not contro, something to its log 1/0 then you can put them to input mode. (some diode is driven to be on when pin is in log.0. It depends whether we need to have this diode still on in stop mode or not. Solution is either to switch it off or set pin to the input mode)

I would like to suggest you to read chapter 14 from AN3262 and search for keyword stop through the document.

https://www.nxp.com/docs/en/application-note/AN3262.pdf

Also some note from a colleague of mine:

During STOP mode, status of pins will be kept unchanged. In this case, the internal pull selection needs to be aligned to the external voltages to avoid additional current consumption in STOP mode.

Leaving input pins floating will cause the pin voltage to float to any voltage depending upon leakages to ground and the supply. Noise will cause the CMOS inverter or gate to which the input is connected to go into an indefinite and high-power dissipation mode, with both N- and P-channel outputs conducting.

Based on this effect, external noise can cause the input stage to switch states at high-frequency (oscillations). Switching from one state to the other will add additional current consumption to the static leakage current. Also, an increased level of noise gets injected to the microcontroller.”

Best regards,

Ladislav