ST7FLITE05M6 power up problem.

[y2399]

Posted on March 01, 2006 at 10:39

ST7FLITE05M6 power up problem.

[y2399]

Posted on February 28, 2006 at 05:44

Hi all and thanks for reading this post.

We are using an ST7FLITE05M6 microcontroller with internal RC oscillator à 1MHz and Low Voltage Detector (LVD) function. We have problems with some of our products, infact the programm don't start at power up. In fact we are using LVD with medium voltage thersold. When Vdd increase from 1V to 5V, the LVD seems to be ok because Reset pin go to high level when Vdd become higher to 3,6V. So reset is OK but programm don't start. When the power is off, Vdd decrease very Slowly and Reset pin go to low level when Vdd become lower than 3,4V. Then continue to go down until a residual stress ranging between 0,5 and 1V. This stage we can start again the program by doing a short circuit on Vdd during several seconds in order tio discharge all capacitors and cancelling the Vdd tension. This problem d'ont uccur on all our boards. Did you already have experience of this problem? I thank you by advance for your assistance.

[henrik239955]

Posted on February 28, 2006 at 06:35

Hi,

I had the same problem with another ST7 mcu. I switched from software watchdog (enabled by software) to hardware watchdog (allways enabled). After that it allways starts up ok! So, if you have software watchdog you can allways try hardware... BR bood

[y2399]

Posted on February 28, 2006 at 10:43

Hi Bood and others,

Thank you very much for your answer. In fact I'm using software watchdog but I don't see the relationship with microcontroller power up. Nevertheless, I can try to test my application with the active hardware watchdog, normally, I should not have modification to make in the program. The problem is that it is not easy to reproduce the defect. I also could note another problem. It happens that the microntroller enters an unspecified state, indeed the pine reset remains in a high state including when the Vdd voltage becomes lower than the threshold voltage of the LVD and passes by again with the top. In this case of figure, I have the impression that the oscillator does not function because of very low consumption of the microcontroller.

[henrik239955]

Posted on March 01, 2006 at 04:33

Hi,

An hardware watchdog is enabled immediately after reset. That means the watchdog will cause a reset at any malfunction at power up. Thats the point with hardware watchdog. /Bood

[y2399]

Posted on March 01, 2006 at 06:31

Hi Bood and others,

Thanks for your explaination. In fact, maybe it can be the solution. After some research, I found an other possible cause to my problem. In fact, it is written at page 14 of the datasheet that the ICCCLK pin (PA6) must be pulled-up internally or oexternally in order microcontroller to avoid entering ICC mode unexpectedly during a reset. But I don't know if the MCU can enter ICC mode only at power up reset or power up and power down reset are concerned. In fact, on my board, PA6 cannot be pulled up, so i'm asked 2 question: 1. if MCU enter in ICC mode, will the hardware watchdog will work and generate an MCU reset to leave ICC mode and restart the software ? 2. is it possible to configure dynamically pin PA6 in order to configure it in pull-up mode in normal time and to leave it floating before each port reading? Many thanks in advance for your help.

[henrik239955]

Posted on March 01, 2006 at 07:46

Hi again,

What do you use PA6 for in your application? If I have understand this right its ok to use PA6 as output, input with internal pull-up or floating with external pull-up. I think you should avoid to have it floating without any external pull-up. Do you need to have it floating? I dont know if the watchdog cause reset at unexpected entering ICC-mode. But I sure think so. /bood

[y2399]

Posted on March 01, 2006 at 10:39

Hi again,

In my application, the PA6 pin is used to monitor a digital voltage (0 or 4,7V) and I cannot use internal or external pull up resistor on this pin without disturbing the signal. STMicroelectronics explaination is a little bit ambiguous because I don't understand if the ICCCLK pin can be used as standard push-pull output or if we must use an external pull-up resistor including if the pin is used at output. As a last resort, I can possibly reverse 2 pines to use PA6 as an output.