Microcontrollers tend to be focused on a specific function, therefore while they're really variable units these days, there are a number of various (often conflicting) alternatives for how you might need the hardware to work. You might think this setting is completed in computer software, but what if you'd like the electronics to act a certain way from ab muscles start? Keeping in mind that Microchip PIC devices can "boot" in a subject of milliseconds, there needs to become a way you telling the electronics how exactly to behave in advance of it beginning up. This information addresses how to truly get your microcontroller based project functioning how you expect when it begins up.
Enter config parts, or, as they was previously called, config fuses. Back in the times when microcontrollers were program-once devices, you truly did strike a blend to be able to plan them. Today, most micros have flash memory that may be developed thousands of instances, but you will find still one-time-programmable (OTP) devices about.
Whatever the case, there's a lot of "config words" that determine the way the micro is going to behave from the get-go. Let's search at several of those choices (we'll select the PIC18F2620 being an example) and then see how to plan them. Sourceboost gives you all of the config strings in a ready-to-use format for including in your project. The structure has the config bits suffixed with exactly the same name while the config term so you can make sure that the proper bits are getting in the best word. Needless to say, your config phrases will be various if you're employing a different microcontroller, but you ought to learn enough here to point you in the proper direction.
In the 18F2620, the config portions are kept in thumb, but at a top storage location. They're located at 0x300001 and upwards. For historic reasons because of the way storage was once fixed on PIC microcontrollers, config words are numbered with each quantity having a "high" and "low" byte.
CONFIG1L doesn't occur on the 18F2620. When it did, it would stay at 0x300000 location.
CONFIG1H includes pieces that specify oscillator options. Typically, in Embedded Activities tasks we use and try external deposits which provide more accurate and reliable results. This does burn up two pins however, and occasionally these could be more important compared to the pace at that the processor is running. The additional gem oscillator is called the HS oscillator (if you're doing the conventional thing of seeking to run the micro as quickly since it may go). In the 18F2620, you can even allow the PLL element which provides you with a four-times pace boost. From CONFIG1H will also be choices to enable the fail-safe clock monitor (that buttons to the inner oscillator should the outside one fail, and an option to enable the switching between different oscillator sources.
We usually recommend that you utilize an additional crystal, and switch off any oscillator switching / failover modes. In prototyping, it is very important to possess trusted, repeatable benefits (mostly to help you decrease the axes of error). It is possible to manage the 18F2620 to start up using the central oscillator (which runs at 8Mhz, or 32Mhz with the PLL enabled) and then move to the additional one (we make use of a 10Mhz gem with PLL permitted giving you 40Mhz). That offers you quicker start-up from interrupts in sleep method or on bootup, if that's important, except for prototyping, this is generally perhaps not necessary.
Our proposed config sequence for CONFIG1H:
#pragma DATA _CONFIG1H, _OSC_HSPLL_1H & _IESO_OFF_1H & _FCMEN_OFF_1H
openbullet config brown-out reset and the power up timer. Brown Out Reset (or BOR) is the power for the microcontroller to reset it self if the supply voltage falls under a given threshold. It will remain in reset state before the offer extends back on the threshold. This can mean some battery preserving (at least, once the battery is level beyond a particular stage, it'll end wearing power as quickly) - but at that time there's number performance available anyway. The ability on timer waits on original power-on for the source to move over the BOR voltage threshold, then weighs about for another 65ms before kicking things down for real. It will help guarantee that the power supply is constant before attempting to accomplish any code.
We've seen some pretty unstable effects from the 18F2620 when testing some LED display panels. We believed the application was piling or resetting the micro when actually, the thing that was happening was the BOR had been tripped as more LEDs were lit and the ability offer dropped. As such, unless you've got a real dependence on it, we suggest converting it off. Causing the energy supply to be in before starting the firmware, is generally advisable (you're not likely going to notice the 65ms it takes).
#pragma DATA _CONFIG2L, _BOREN_OFF_2L & _BORV_2_2L & _PWRT_ON_2L
CONFIG2H provides you with controls for the watchdog timer. This can be a timer that resets the PIC in a quantity of time (you can generally establish how long that will be). It could be great want to reset your PIC if you're doing something from that you might never retrieve - although hopefully you're prepared sufficient rule that can't occur! Alternatively, the watchdog timer can also draw the PIC out of sleep mode. This implies you are able to organize for the PIC to get to sleep for a specific amount of time (if nothing else happens). For prototyping, we recommend switching the watchdog timer off. Should you choose help it, ensure you reset the watchdog timer regularly or - effectively, you are able to guess what'll happen.
#pragma DATA _CONFIG2H, _WDT_OFF_2H & _WDTPS_128_2H
CONFIG3H has a collection of setup items. You can choose for the RE3 flag to be accessible (as insight only) and for that pin to be MCLR (which resets the micro when taken low). For prototyping, to be able to reset the micro by pushing a key now is easier than taking the energy out.
The LPT1OSC bit offers the possibility of a "large power" setting or perhaps a "reduced energy mode" ;.The reduced energy method is more sensitive in high noise environments. So if battery use is very important, you will need to create your world carefully. For prototyping, needless to say, we would suggest leaving that in large energy mode.
PBABEN, enables you to establish if PORTB pins 0 - 4 must wake up as analog insight hooks or electronic hooks upon reset. Needless to say you are able to modify this in computer software in the ADCON1 enroll at any time.
The CCP component is just a Capture / Examine / PWM component and one last CONFIG3H touch enables the "steering" of the result to be on either RC1 or RB3. This really is practical to be able to modify in the event that you require the other functionality available on one of these brilliant pins (RB3 can also be analogue insight 9 and RC1 can be Timer 1 oscillator input). As an alternative, your PCB structure could be easier if you might shift this productivity to one or the other. For prototyping, generally that doesn't subject either way.
#pragma DATA _CONFIG3H, _CCP2MX_PORTC_3H & _PBADEN_OFF_3H & _MCLRE_ON_3H
CONFIG4L contains some interesting alternatives and shows really obviously how crucial it's to manage to arrange the PIC before startup.
The DEBUG bit allows electronics debugging. You can stage through rule, collection breakpoints and so on - if you have your computer software collection properly and that bit cleared. Electronics debugging also involves the exceptional use of RB6 and RB7 (also useful for ICSP programming). In all loyalty, we discover that serial productivity is usually adequate to get insects, while you can debug plenty of PICs with simply a PicKit2.
XINST enables the 18F prolonged training collection mode. This isn't employed by Sourceboost and if you switch it on in error (regardless of the compiler you're using) you will have some pretty unstable results. Among our readers spent times searching for what was wrong along with his rule simply to realize the XINST touch was set.
LVP provides you with the capacity to plan the PIC using ICSP without requiring the "higher" Vpp voltage. There is a get nevertheless - you need to commit the RB5 pin (PGM) to being an sign if you should be in development style or not. Provided the PicKit2 provides the right voltage anyway, there doesn't be seemingly plenty of price in changing this on for prototyping purposes.
Eventually, the STVREN gives the possibility of experiencing the PIC reset if the heap overflowed or underflowed. If, for example, you contact too many stacked functions, it would allow the PIC to reset. Once reset, you are able to study why the PIC reset and report a fault. We recommend causing that on - if your PIC shoes in the center of doing something, you can reasonably assume that you've used up the heap place (possible when you're serious in a stacked situation and then an interrupt occurs).
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