A watch-dog’s work is causes the embedded processor or the micro controller can, in carries on the response after the invalid software condition may reposition. In the network application, the system work cannot interrupt, the watch-dog in guaranteed that the system did not freeze or jumps out the endless loop in the work to play a strong character.
Figure 1 watch-dogs and so on Maxim MAX6746 have played the strong character
The high rank network function brings the question is the system needs many clocks. Perhaps a simple watch-dog is insufficient. When uses impractically massively based on hardware’s timer, one batch of network timer equated in using the clock interrupt signal, but all clocks maintained in the software. However, in many applications, the hardware timer still could provide the solution which may trust.
Usually, the embedded software has one to be able to transfer the different subroutine the main loop, the watch-dog, once will occupy the main loop the peak to reposition. If the main loop cannot carry out correctly, the watch-dog will start, will then cause the component to reposition. Because many network applications the watch-dog joins becomes reliable. But a watch-dog cannot survey directly wrongly, said accurately, the watch-dog must before it repositions the processor achieves the initialization time-gap the apex.
The watch-dog may lay aside among the micro controller, for instance looks like MAXQ2000, outside sets in standard single IC or the bedded system achievement supports ASIC a part. The built-in watch-dog can economize, but loses control easily the code affects. The exterior watch-dog has an independent clock pulse source, this makes its reliability to increase greatly. If disposes correctly, they will not be lost control the code to bypass or invalid.
A usual effective watch-dog function is “the window” or “the minimum/maximum value”, when the watch-dog is controlled too slow or is too quick, this function can through send the reset signal to strengthen to the proper operation authentication. When if the clear spatial counter register’s instruction arrives counter register’s quantity has not reached the threshold value, the component will trigger the system reset. This has not only prevented the software bug, but can also in the crystal oscillator by wrong frequency work time repositions MPU. Another function is forbids the watch-dog through the exterior logical input or the internal register position.
Built-in MCU watch-dog
For example, we look at the MAXQ2000 internal watch-dog. If is not controlled, this watch-dog will trigger an interrupt, after counting 512 extra system clock cycles will reposition.
This interrupt has provided the final opportunity for the memory debugging information, it is in the electric circuit development and the failure diagnosis a very useful function. Has substituted for the memory debugging information, this interrupt can use for to reply from the breakdown wrong and the clear spatial watch-dog.
Other built-in watch-dogs are likely same, MAXQ2000 can also terminate through the software. However this function is the double-edged sword, because the out of control code will forbid the watch-dog, and will continue chaotically noisy.
A slightly controller connects theirs watch-dog the independence on system clock’s crystal oscillator. Although MAXQ2000 watch-dog from system clock, but the electric circuit will still cut on the spare RF oscillator to prevent the main crystal oscillator losing control.
Outside puts in MCU watch-dog
Many manufacturers can provide have many kinds of function special watch-dog IC. For instance MAX6752, has the window function, may let the user adjustment watch-dog’s overtime region, and sets at the electric capacity with outside to adjust the reset pulse.
On the watch-dog MAX6369 logical input base pin can forbid the clock, the impediment replacement. Although connects the micro controller with the logical base pin is very appealing, but will bring the risk to the system, because the out of control code can forbid the watch-dog stochastically. Usually, when the micro controller starts, the watch-dog must in the unloading phase forbid. MAX6369 can the time which finished in the replacement provides an extra long watch-dog cycle. When the watch-dog first time is started, normal will continue the overtime to return. Some timers can also provide one to vibrate and the ESD protection reset switch input.
