What are the situations which would cause an MCU to not turn ON?

[yonathan]

Hello,

My company has been using an MC9S08QG8 MCU in one of our products for years and most recently during production, it was found that maybe 1/100 times when resetting AC Power, there would be no response from the MCU. But even once that happens once you reset the AC power the unit will continue to work normally.

One of the initial steps in the program during variable initialization is to set the PWR LED ON but the manufactures has informed us that the LED is not ON during this situation which means the MCU is Off and did not start.

The Manufacturers also informed and showed us graphically VDD is stable and 3.3V.

I have also informed them to check if the Reset Pin on the MCU is Held in a reset state (GND <~1.5V) and it is not.

We have also confirmed that the MCU is real and not a fake clone since we are getting it from a reliable distributor.

If anyone has experienced a similar problem any advice will be useful.

Thanks in advance!

[yonathan]

Hello Tony,

From my understanding of the LVD Reset the MCU will only be held in reset until the supply voltage has risen above the level in LVDV. I checked the program and LVD reset is enabled and LVDV is set to the high trigger voltage 3V:

   -   SPMSC1:   00011100 (Set Bits:   LVDRE + LVDSE + LVDE) 

   -   SPMSC2:   00000000

   -   SPMSC3:   00110000 (Set Bits:   LVDV + LVWV)

When this problem occurs it has been verified that the supply voltage is stable and above 3V (3.3V) but there is still no response from the MCU.

I have also tested on the actual product by reducing the supply voltage to <2V (the MCU does reset) and then increasing the voltage to 3.3V. Once the voltage returns to 3.3V the MCU begins to operate normally so I dont think this is the problem.

Do you have any other suggestions?

[tonyp]

Have you set LVD reset correctly for your case?

5.6.2 LVD Reset Operation
The LVD can be configured to generate a reset upon detection of a low voltage condition by setting
LVDRE to 1. After an LVD reset has occurred, the LVD system will hold the MCU in reset until the supply
voltage has risen above the level determined by LVDV. The LVD bit in the SRS register is set following
either an LVD reset or POR.