What is the expected status (High/Low) of Port P and S pin when the S12ZVL comes out of reset?

[kumarsaket]

What is the expected status (High/Low) of Port P and S pin when the S12ZVL comes out of reset? I am testing the controller in and around the Low Voltage Assert (2.95V) to Low Voltage De-assert (3.13V) range. I see that when supply voltage exceeds 3.13V,  Port S and P go high momentarily and automatically come down. I am using these port pins as output and they have been initialized to 0 in the code.  

Additionally I also observe that at for Supply Voltage between 2.95V - 3.13V, the pin PS3 toggles constantly. What could be the reason for this behavior?

[RadekS · Accepted solution]

Hi Kumar,

Please look at Table 1-6. Pin Summary in RM.

This table defines default state of pin right after reset.

Both P and S ports are defined as Off. It means that they are configured as a digital input (that is common for all GPIO pins) without internal pull-up/down = floating input.

So, from this point of view, the voltage level at these pins will be strongly influenced by connected external devices at these pins. If you need manage, that these pins will have specific voltage level when MCU reset and prior output is enabled, you must use an external pull-up or pull-down.

Note: I would like to recommend do not leave unused GPIO pin floating. This may cause higher power consumption when pin input voltage is in the linear area near to VDDX/2. This is not valid for port AD until we enable digital input pin buffer in DIENAD register.

You didn‘t specify how PS3 pin is configured by your code. This toggling may be caused by two effects.

When PS3 is in the default state (floating input), the result voltage level is given by the combination of MCU and test equipment leakage currents.

The voltage 3.045V is right at edge of Low Voltage Interrupt. So, I suppose, that MCU may periodically enter and leave reset state and you simply see Low Voltage assert and deassert hysteresis. These minimal waves at power supply may be caused by simple charging/discharging blocking capacitors (The MCU have probably higher power consumption in a run mode in compare with reset state).

I hope it helps you.

Have a great day,
Radek

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[kumarsaket]

Hi Radek,

Thanks for the reply, it helped me narrow down to the problem. I have configured the pin PS3 as output. You are right, I need to externally pull-up or pull-down to make my circuit work the way I want.

Thanks again.

Kumar