I had written about interrupts in the post here. This post is specifically about a particular interrupt which in most cases in Non-Maskable. The word Non-Maskable tells us that come what may the µC software will not be able to avoid it. This special interrupt i am talking about is "Reset".
Is Reset an Interrupt?
It is technically an interrupt however, some people feel that it is a microcontroller state. This is because when the µC is in Reset it really cannot do anything useful because the code will not be executed. However, we state it is as an interrupt because of the following reasons perhaps
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Is Reset an Interrupt?
It is technically an interrupt however, some people feel that it is a microcontroller state. This is because when the µC is in Reset it really cannot do anything useful because the code will not be executed. However, we state it is as an interrupt because of the following reasons perhaps
- There is a place for the Reset in the Interrupt Vector Table(IVR)
- There are different reasons for reset to occur and in some µC's all the reasons cause the code to branch to the above mentioned vector.
What are the different types of Interrupts?
The most commonly known is the Power-On-Reset (POR) as it is commonly known in the embedded world. Note that just by applying power it is really not gaurenteed that the micro controller is undergoing a RESET. This is a very common mis-understanding that if we just apply power for the first time the micro will be under going a POR. For a µC to really under a proper reset it is needed that RESET pin is correctly handled. This is done via a reset circuit which looks like this. Note that this is for a 8051 micro which for some reason is RST high, compared to the conventional micro controllers where this is active low.
The other type which happens very frequently if you are a bad programmer like me is the Running reset. A running reset can be caused by many different sources. These include Watchdog reset, Illegal opcode reset, Illegal memory access reset and finally software reset. Each of these will be discussed in greater detail in the coming posts. As of now it is sufficient to know that this occurs because of something bad that has been caused in our software or in some cases we intentionally did it ( because we feel the best way is that way!!). In both cases the CPU starts from the Reset vector and starts executing code ( Except for in higher end 32 bit micro's where Reset vector is not the only criteria!!). Of course it is also useful to note that some µC's provide various vectors for WDT reset, Illegal opcode reset (PowerPC from Freescale is an good example).
Reset handling is a tricky issue for the hardware designers and not so much for the software guys. In coming posts, I will talk about some of the issues i have observed.
The most commonly known is the Power-On-Reset (POR) as it is commonly known in the embedded world. Note that just by applying power it is really not gaurenteed that the micro controller is undergoing a RESET. This is a very common mis-understanding that if we just apply power for the first time the micro will be under going a POR. For a µC to really under a proper reset it is needed that RESET pin is correctly handled. This is done via a reset circuit which looks like this. Note that this is for a 8051 micro which for some reason is RST high, compared to the conventional micro controllers where this is active low.
The other type which happens very frequently if you are a bad programmer like me is the Running reset. A running reset can be caused by many different sources. These include Watchdog reset, Illegal opcode reset, Illegal memory access reset and finally software reset. Each of these will be discussed in greater detail in the coming posts. As of now it is sufficient to know that this occurs because of something bad that has been caused in our software or in some cases we intentionally did it ( because we feel the best way is that way!!). In both cases the CPU starts from the Reset vector and starts executing code ( Except for in higher end 32 bit micro's where Reset vector is not the only criteria!!). Of course it is also useful to note that some µC's provide various vectors for WDT reset, Illegal opcode reset (PowerPC from Freescale is an good example).
Reset handling is a tricky issue for the hardware designers and not so much for the software guys. In coming posts, I will talk about some of the issues i have observed.
Wanna add your point or provide more info ? Please leave your comment. You can subscribe to this blog by using the links under "Subscribe" section.
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