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 Microcontrollers tend to be focused on a certain function, therefore while they're very variable products these days, you will find numerous different (often conflicting) options for how you may need the electronics to work. You might think that this setup is done in application, but what if you want the hardware to behave a particular way from ab muscles start? Bearing in mind that Microchip PIC units may "boot" in a subject of milliseconds, there needs to be a way you showing the hardware how exactly to act in advance of it beginning up. This short article covers how to truly get your microcontroller centered project functioning how you assume when it starts up.

Enter config portions, or, as they used to be called, config fuses. In the times when microcontrollers were program-once devices, you truly did blow a fuse in order to program them. Nowadays, many micros have flash storage that can be programmed tens of thousands of times, but there are still one-time-programmable (OTP) products about.

Whatever the case, there's a lot of "config words" that define how a micro will probably behave from the get-go. Let's look at a few of these options (we'll pick the PIC18F2620 being an example) and then see how exactly to program them. Sourceboost offers you all of the config strings in a ready-to-use structure for including in your project. The structure has the config bits suffixed with the exact same title whilst the config term so you can make sure that the proper bits are going in the right word. Of course, your config phrases is likely to be various if you're utilizing a various microcontroller, but you ought to learn enough here to place you in the right direction.

In the 18F2620, the config parts are saved in display, but at a higher storage location. They're kept at 0x300001 and upwards. For traditional causes because of the way memory was previously fixed on PIC microcontrollers, config phrases are numbered with each number having a "high" and "low" byte.

CONFIG1L doesn't exist on the 18F2620. If it did, it would live at 0x300000 location.

CONFIG1H includes bits that establish oscillator options. Usually, in Stuck Activities projects we use and try additional deposits which give more appropriate and trusted results. That does consume two pins but, and often these can be more essential compared to the speed at that your processor is running. The external gem oscillator is referred to as the HS oscillator (if you're doing the typical point of seeking to operate the micro as fast since it may go). In the 18F2620, you may also allow the PLL component which provides you with a four-times pace boost. From openbullet config may also be choices to enable the fail-safe time check (that changes to the internal oscillator if the outside one crash, and an option allow the converting between various oscillator sources.

We generally recommend that you utilize an external gem, and switch off any oscillator changing / failover modes. In prototyping, it is essential to own reliable, repeatable benefits (mostly to help you reduce the axes of error). It is possible to arrange the 18F2620 to set up using the internal oscillator (which goes at 8Mhz, or 32Mhz with the PLL enabled) and then change to the additional one (we work with a 10Mhz crystal with PLL permitted giving you 40Mhz). That provides you faster startup from interrupts in rest setting or on bootup, if that's important, except for prototyping, this really is typically maybe not necessary.

Our advised config string for CONFIG1H:

#pragma DATA _CONFIG1H, _OSC_HSPLL_1H & _IESO_OFF_1H & _FCMEN_OFF_1H

CONFIG2L handles brown-out reset and the power up timer. Brown Out Reset (or BOR) is the capability for the microcontroller to reset it self if the supply voltage comes under a specified threshold. It'll stay in reset state before supply goes back over the threshold. This will mean some battery preserving (at least, when the battery is flat beyond a certain level, it'll end draining energy as quickly) - but at that point there's no performance accessible anyway. The ability on timer waits on original power-on for the offer to get above the BOR voltage limit, then hangs about for still another 65ms before throwing things down for real. This assists assure your power is continuous before trying to implement any code.

We've seen some very unknown results from the 18F2620 when testing some LED present panels. We believed the application was piling or resetting the micro when in fact, the thing that was occurring was the BOR had been tripped as more LEDs were lit and the power present dropped. As such, unless you've got a genuine need for it, we recommend switching it off. Causing the power present to settle prior to starting the firmware, is usually advisable (you're most likely not planning to notice the 65ms it takes).

#pragma DATA _CONFIG2L, _BOREN_OFF_2L & _BORV_2_2L & _PWRT_ON_2L

CONFIG2H offers you options for the watchdog timer. This is a timer that resets the PIC in a certain amount of time (you can largely specify how long which may be). It may be good want to reset your PIC if you're doing anything from which you may never recover - although ideally you're written adequate code this can't occur! As an alternative, the watchdog timer may also pull the PIC out of sleep mode. What this means is you can arrange for the PIC to go to sleep for a certain amount of time (if nothing otherwise happens). For prototyping, we suggest switching the watchdog timer off. Should you allow it, be sure you reset the watchdog timer regularly or - well, you can imagine what will happen.

#pragma DATA _CONFIG2H, _WDT_OFF_2H & _WDTPS_128_2H

CONFIG3H has a collection of configuration items. You can pick for the RE3 green to be accessible (as insight only) and for that flag to be MCLR (which resets the micro when taken low). For prototyping, to be able to reset the micro by pressing a key now is easier than taking the power out.

The LPT1OSC bit offers the choice of a "high power" function or a "minimal energy mode" ;.The reduced energy function is more sensitive and painful in high sound environments. So if battery usage is very important, you need to design your enterprise carefully. For prototyping, of course, we would recommend making this in large power mode.

PBABEN, lets you specify if PORTB pins 0 - 4 should get up as analog feedback hooks or electronic hooks upon reset. Needless to say you can modify this in pc software in the ADCON1 register at any time.

The CCP element is just a Capture / Examine / PWM component and one last CONFIG3H touch allows the "steering" of the production to be on both RC1 or RB3. That is handy to have the ability to change in the event that you require the other operation on one of these brilliant hooks (RB3 can be analogue insight 9 and RC1 can be Timer 1 oscillator input). Instead, your PCB structure may be easier if you may shift this output to 1 or the other. For prototyping, usually that doesn't subject both way.

#pragma DATA _CONFIG3H, _CCP2MX_PORTC_3H & _PBADEN_OFF_3H & _MCLRE_ON_3H

CONFIG4L includes some fascinating alternatives and reveals really clearly how essential it's to manage to configure the PIC before startup.

The DEBUG bit enables electronics debugging. You can step through signal, set breakpoints and so on - when you yourself have your software collection properly and this touch cleared. Electronics debugging also involves the unique utilization of RB6 and RB7 (also employed for ICSP programming). In all integrity, we realize that successive productivity is generally ample to find insects, although you can debug lots of PICs with only a PicKit2.

XINST permits the 18F expanded training collection mode. This isn't used by Sourceboost and in the event that you switch it on by mistake (regardless of the compiler you're using) you will see some fairly unknown results. Among our viewers spent days trying to find that which was wrong along with his signal only to realize the XINST touch was set.

LVP offers you the capability to plan the PIC applying ICSP without requiring the "higher" Vpp voltage. There is a catch but - you'll need to commit the RB5 flag (PGM) to as an indicator if you are in programming mode or not. Given the PicKit2 provides the best voltage anyhow, there doesn't appear to be a lot of value in converting this on for prototyping purposes.

Finally, the STVREN offers the possibility of having the PIC reset if the heap overflowed or underflowed. If, for example, you contact way too many nested operates, it would allow the PIC to reset. Once reset, you are able to study why the PIC reset and report a fault. We recommend leaving that on - if your PIC shoes in the middle of performing anything, you can reasonably think that you've utilized the heap place (possible when you're heavy in a stacked situation and then an disturb occurs).