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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.
if the internal watchdog is properly enabled, it will cause a reset when it is not updated for any reason. What I said is both the external and internal watchdogs to be used together to handle such situations. -internal to avoid running in an infinite loop and external to handle the situation where the program is not at all running and internal WDT not running.
Why complicate the issue?
IF you have an external watchdog, why not let it handle both situations?
"handle the situation where the program is not at all running"
Do you have any reason to suspect that this is actually happening in your case?
Yes. May be due to voltage spikes the program stops. After doing some additional filtering, this problems seems to be solved. But still I wanted to take an extra precaution.