ST7FLITE29, RESET not working

delser9 · ‎2006-03-07

Posted on March 07, 2006 at 11:46

delser9 · ‎2005-08-03

Posted on August 04, 2005 at 06:03

Hi,

we have a problem with the ST7FLITE29. While turning our application on and off, sometimes the ST7 gets stuck. In these cases even pulling down the RESET pin to GND does not restart the controller. Watchdog does not solve the problem either. Only completely pulling Vdd down to GND helps restarting the circuit.

Has anybody an idea what may be wrong with our application?

Thanks a lot

Alfredo

wolfgang2399 · ‎2005-08-03

Posted on August 04, 2005 at 06:56

Hi Al,

first of all: how do you drive your reset 'input'?

Because you must not drive it with a pushpull output like a normal CMOS-gate. But to drive your reset take an open collector/open drain device with an additional pullup resistor as nessecary.

If your gate is trying to pull the input port to a high level, perhaps it will win over the pulldown transistor in your ST7Lite29.

Further information in the datasheet:

- page 27: Figure 15. Reset Block Diagram

- page 110: Chapter 13.9.1 Asynchronous RESET Pin

WoRo

delser9 · ‎2005-08-03

Posted on August 04, 2005 at 08:08

Hello WoRo,

in our application the RESET pin is driven by the LVD. There is no external RESET. It has only a 10pF capacitor to GND, as the datasheet suggests it.

The external RESET we described is done manually, pulling down the RESET to GND. (So there is no CMOS output connected to the RESET pin.) In the application we don't need that kind of RESET. It's done only for restarting the stuck ST7.

We just cannot immagine why that kind of manual RESET does not restart the ST7. Only a power down may restart it...

Best regards

Alfredo

wolfgang2399 · ‎2005-08-04

Posted on August 04, 2005 at 09:37

Alfredo,

sorry I've no further idea.

As you say the ''Watchdog does not solve the problem either'' I'd like to bring you to one mysterious phenomena which I recognized in my application:

With a crystal oscillator, a disabled PLL and selected PLLx4 the watchdog won't work at all, with PLLx8 and also disabled PLL - really!!! - it works.

Perhaps that helps you tracing on another way.

WoRo

delser9 · ‎2005-08-04

Posted on August 05, 2005 at 08:53

Thanks WoRo for your time and help.

But our problem is still unsolved. We are wondering if there are any ST guys caring about their customers problems. Whenever we ask for support the ST product manager simply points us to that ST7 forum. But all the help we get is that of other customers who have their own problems.

WHERE ARE THE ST SUPPORT ENGINEERS ???

It is for YOU that we are repeating our question:

How is it possible that a ST7LITE29 gets stuck during start up and cannot be restarted by an external RESET (short circuit between RESET pin and GND pin), but only by a power shut down?

That problem appears only once out of about twenty startups. In all the other cases everything is working fine. That shows that our circuit and program are on principle working correct.

Please help! Thanks!

Al

alok2 · ‎2005-08-07

Posted on August 08, 2005 at 04:03

Dear Al_Capone,

What is the Oscillator used and option bytes ? Did you check if the application respects the Table 23. List of valid option combinations ? What exactly is VDD rise & fall time. Does it respect the LVD VtPOR ?

BTW, why are you using id as ''moderator'' ;-))

delser9 · ‎2005-08-07

Posted on August 08, 2005 at 07:10

Dear alok

1) We use the internal RC oscillator.

2) LVD is enabled, watchdog is by software.

3) Table 23 is respected.

4) Vdd rise time is 1250 us/V. That means it respects VtPOR.

5) I have no idea why I should be a moderator. Can you tell me how I can 'switch off' the moderator sign?

Thanks, and best regards

Al

alok2 · ‎2005-08-08

Posted on August 09, 2005 at 02:27

What is Vdd for device and the voltage upto which Vdd decreses before rising again. I wonder why LVD reset is not produced when voltage is changing.

You said you have connected 10pf on reset. It should be 10nf as per datasheet, Is it a typo ?

for 'Moderator' name, i dont know what's the problem with your configuration, can you try to modify your profile ?

delser9 · ‎2005-08-08

Posted on August 09, 2005 at 04:34

Dear alok

1) Yes you are right, 10pF was a typing error. It's a 10nF in our circuit, so that's not the problem.

2) Vdd is 5.3V, which is correct according to the datasheet.

3) After the ST7 worked correctly, we decrease the voltage to about 1.0V (means: far below the highest voltage threshold!) and then try to restart it again by increasing the Vdd to 5.3V. Most of the time it works fine. But sometimes the ST7 stucks. Once the ST7 stucks, it is impossible to restart it otherwise than by pulling the Vdd to zero. Pulling Vdd down to 1.0V doesn't help. It must be zero!

4) Actually we don't think the LVD has any influence on that behaviour. We expect that an external Reset has always priority on every other software or hardware configuration. So why it doesn't work in our case?

'Moderator' problem: where in the profile? I don't see any box concerning the 'moderator'. BTW: Didi you realize that the 'Moderator' sign doesn't appear in the public forum but only in the 'reply' window?

Best regards

Al