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Hi, I use AT89S52 in a project. I send and receive data through TXD, RXD pins to a GSM module for sending SMS to another mobile equipment. I use watchdog facility and the watchdog counter is reset at every 256 counts. My crystal frequency is 11.0592 MHz. It happens once in a while that the uC doesn't respond and remains as if it hangs. Then it has to be RESET again. I doubt whether it happens while serial data reception and sending happens simultaneously. I wrote the program in C using KEIL IDE. My questions are 1) What are the special precautions to be taken in this case?(sending and receiving simultaneously) 2)why this happens even when the watchdog is active? It will be highly appreciated if anybody can give some guidance.
All O/P pins high is the default situation.
All O/P pins high at reset
this thread has been going on for a long time and it is time for "exotic guesses"
one such would be that you hang on a non-initialized variable that by sheer coincidence happens to be good when the processor powers up (memory at power on is random) and makes you hang when a WD reset happens (where the memory contents are preserved).
Erik
1)It never went to a hang situation while switching ON. 2)It never went to such situation when tested in my place (actual working condition is electrically noisy) 3) I initialized all variables. Do you think that spikes in suply line OR RESET pin can cause similar situation?
OP: I think he might be suggesting you are using an uninitialised variable somewhere in your code. But I'm not too sure.
2)It never went to such situation when tested in my place (actual working condition is electrically noisy)
the methods to handle noise sensitivity are described here www.8052.com/.../119926
CLEARLY you have TWO problems a) you are noise sensitive b) you either miss a supervisor or your WD is handled wrong.
Yes!
That is precisely why a large variety of Supervisor circuits is widely available from a number of manufacturers...
Many of these also include a hardware watchdog...
You're not using an RC reset generator, are you...?
For resetting during switch ON, I used an RC network with 10uF and 10K. But today I changed it to a single 0.1uF capacitor connected from Vcc to RESET pin. It works. I expect that this will make some improvement as far as sensitivity to power supply spikes are concerned.
Thank you for the useful link. But I don't know whether I can conclude that it is a noise related problem. Right now I am inclined to believe so.
You mean, you've tried it a couple of times on your bench, and you haven't noticed any problems?
That is not anywhere near a sufficient amount of testing to guarantee that it will always work under all conditions of power supplies, noise, etc, etc,...
You should understand this by now: you said you'd already tried it on your bench with no problems, and the problems only arise in the Real World - so it should be obvious that your bench is not a good simulation of the Real World!
The whole purpose of a Supervisor chip is to cope with these kind of Real World situations that don't occur in nice, clean bench tests and are not covered by simplistic RC reset circuits...
You should understand this by now: you said you'd already tried it on your bench with no problems, and the problems only arise in the Real World - We were discussing this as if a program bug. I also thought it is so. I pass this additional details expecting that experienced people may give some useful hints. It is not that I am unaware about new problems that can come in the real world.
For resetting during switch ON, I used an RC network with 10uF and 10K. no wonder your have problems INSTALL A SUPERVISOR CHIP
Normally what among the below can happen with a spike in RESET pin OR any other pin 1)uC will go to default condition (in this case all O/P high) and remain like that 2)The program will stop and remain where it was before hang up. 3) Result is totally unpredictable.
In my case my observation is that it goes to condition 1. Is it a mere coincidence OR has it got some meaning?
.. that with a RC reset you WILL get 'mysterious' errors on spikes.
When are you going to add that supervisor???
For the units already installed, there is some difficulty in adding a new IC. I will definitely add the supervisor circuit in the next unit onwards. However I am trying to get the supervisor IC and try to implement in the present unit also.
you can get a 'tripod' (a supervisor chip in a 'transistor package') such as DS1233 datasheets.maxim-ic.com/.../DS1233.pdf which can easily be added to an existing board.
NOTE!!!! do not know if the reset poarity of the DS1233 and your chip match DO CHECK. If they do not, there are other 'tripods' that do.
Thank you very much
I tried supervisor IC DS1232. Working well.It has got a watchdog also which is monitoring the ALE pin of my uC. I think, still it is better to use the internal watchdog also to avoid program getting stuck due to software issues. Am I right?