controller.....8051 related

WHY the crystal frequency is selected 11.059MHz.....any reason??
what is the use of watchdog timer????.....
thanks

11.0592 is used for baud rate purpose.. when you use baud rate formula and calculate using 11.0592 the you get 9600 a round value.. if you use any other value then you get decimal point for baud rate result...

---------- Post added at 17:08 ---------- Previous post was at 17:00 ----------

Watch dog timer is usually inbuilt timer( but there are external WDT also) , whose main work is to monitor the system operation.. A watchdog timer (WDT) is a device or electronic card that performs a specific operation after a certain period of time if something goes wrong with an electronic system and the system does not recover on its own.

A WDT contains a digital counter that counts down to zero at a constant speed from a preset number. The counter speed is kept constant by a clock circuit. If the counter reaches zero before the computer recovers, a signal is sent to designated circuits to perform the desired action.

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If the system hangs or cannot perform the operation on time... then WDT does a soft reset of the system..

A common problem is for a machine or operating system to lock up if two parts or programs conflict, or, in an operating system, if memory management trouble occurs. In some cases, the system will eventually recover on its own, but this may take an unknown and perhaps extended length of time. A watchdog timer can be programmed to perform a warm boot (restarting the system) after a certain number of seconds during which a program or computer fails to respond following the most recent mouse click or keyboard action.

In simple words
A clock circuit that keeps counting from a set number down to zero. If the event it is monitoring occurs before it reaches zero, it resets to the starting number and starts counting down again. If the timer reaches zero, it performs some action; for example, a diagnostic operation such as rebooting the computer or sending an error message.

thank you so much...i got your point....it means we do not let WDT to reach up to zero...if it reach to zero....problem can be occur...hang OR rebooting.......but some times...if the system at its initial starting condition....(just started)...and hanged...what it means...
is wdt working on cell/battery in mother board.....

yes ... you are correct... if any thread or task hangs then it does not reset the WDT . and when WDT underflows the reset happens.........

but remember WDT will only soft reset the system....... its different from hard reset..........