Microcontrollers tend to be focused on a specific function, therefore while they're very variable products these days, you can find several different (often conflicting) choices for how you may need the electronics to work. You might think this configuration is performed in computer software, but what if you would like the equipment to do something a specific way from the begin? Remember that Microchip PIC devices may "boot" in a subject of milliseconds, there wants to be always a way you telling the equipment how exactly to act in advance of it beginning up. This information addresses how to get your microcontroller centered task functioning the manner in which you expect when it starts up.
Enter config portions, or, as they was once named, config fuses. Back in the days when microcontrollers were program-once units, you truly did hit a blend in order to program them. Nowadays, many micros have thumb memory which can be developed countless amounts of occasions, but you can find however one-time-programmable (OTP) units about.
Whatever the case, there's a number of "config words" that define the way the micro will probably behave from the get-go. Let's search at several of those possibilities (we'll choose the PIC18F2620 being an example) and then see just how to plan them. Sourceboost offers you all the config strings in a ready-to-use format for including in your project. The format gets the config portions suffixed with the same title since the config term in order to make sure that the proper parts are going in the best word. Needless to say, your config words is likely to be different if you're employing a different microcontroller, but you need to learn enough here to point you in the right direction.
In the 18F2620, the config bits are located in display, but at a higher memory location. They're saved at 0x300001 and upwards. For historical reasons as a result of way storage once was established on PIC microcontrollers, config words are numbered with each number having a "high" and "low" byte.
CONFIG1L doesn't occur on the 18F2620. If it did, it would live at 0x300000 location.
CONFIG1H contains parts that establish oscillator options. Usually, in Embedded Adventures projects we try and use additional deposits which provide more exact and trusted results. This does burn up two hooks but, and often these may be more essential than the rate at which the processor is running. The additional gem oscillator is referred to as the HS oscillator (if you're doing the conventional issue of trying to operate the micro as rapidly because it can go). In the 18F2620, you can even enable the PLL module which will provide you with a four-times speed boost. From openbullet configs will also be alternatives to enable the fail-safe time monitor (that buttons to the interior oscillator should the additional one crash, and an option to enable the changing between different oscillator sources.
We typically recommend that you employ an additional gem, and turn fully off any oscillator switching / failover modes. In prototyping, it is very important to own reliable, repeatable results (mostly in order to reduce the axes of error). It is possible to manage the 18F2620 to launch using the internal oscillator (which runs at 8Mhz, or 32Mhz with the PLL enabled) and then change to the external one (we make use of a 10Mhz crystal with PLL allowed providing you 40Mhz). That offers you faster startup from interrupts in sleep mode or on bootup, if that's crucial, however for prototyping, this really is usually perhaps not necessary.
Our proposed config string for CONFIG1H:
#pragma DATA _CONFIG1H, _OSC_HSPLL_1H & _IESO_OFF_1H & _FCMEN_OFF_1H
CONFIG2L grips brown-out reset and the power up timer. Brown Out Reset (or BOR) is the ability for the microcontroller to reset itself if the offer voltage comes below a given threshold. It'll stay static in reset state until the present goes back within the threshold. This will mean some battery preserving (at least, after the battery is smooth beyond a certain stage, it'll stop draining energy as quickly) - but when this occurs there's no functionality accessible anyway. The power on timer waits on initial power-on for the offer to go over the BOR voltage threshold, then hangs about for still another 65ms before throwing points down for real. This assists ensure that your power is continuous before wanting to implement any code.
We have seen some very volatile results from the 18F2620 when screening some LED display panels. We believed the program was crashing or resetting the micro when actually, what was occurring was the BOR was being tripped as more LEDs were lit and the ability offer dropped. Therefore, unless you've got an actual requirement for it, we suggest converting it off. Leaving the ability present to be in prior to starting the firmware, is typically recommended (you're not likely going to spot the 65ms it takes).
#pragma DATA _CONFIG2L, _BOREN_OFF_2L & _BORV_2_2L & _PWRT_ON_2L
CONFIG2H gives you options for the watchdog timer. This is a timer that resets the PIC in a specific amount of time (you can generally establish the length of time that may be). It may be excellent plan to reset your PIC if you're doing something from that you may never recover - though preferably you're published good enough rule that this cannot occur! Instead, the watchdog timer can also draw the PIC out of sleep mode. What this means is you can arrange for the PIC to go to sleep for a specific amount of time (if nothing otherwise happens). For prototyping, we suggest changing the watchdog timer off. Should you choose permit it, be sure you reset the watchdog timer regularly or - well, you are able to think what'll happen.
#pragma DATA _CONFIG2H, _WDT_OFF_2H & _WDTPS_128_2H
CONFIG3H has an accumulation setup items. You are able to pick for the RE3 pin to be accessible (as feedback only) or for that green to be MCLR (which resets the micro when pulled low). For prototyping, being able to reset the micro by pushing a switch is simpler than taking the energy out.
The LPT1OSC touch offers the choice of a "high power" function or perhaps a "minimal energy mode" ;.The reduced energy method is more sensitive and painful in large noise environments. So if battery consumption is vital, you will need to create your circuit carefully. For prototyping, obviously, we would suggest leaving this in high power mode.
PBABEN, enables you to establish if PORTB pins 0 - 4 should get up as analog feedback hooks or electronic hooks upon reset. Of course you can modify this in pc software in the ADCON1 register at any time.
The CCP module is a Capture / Evaluate / PWM element and your final CONFIG3H touch enables the "steering" with this result to be on either RC1 or RB3. This really is useful to manage to modify in the event that you require one other performance on one of these pins (RB3 can be analogue feedback 9 and RC1 may be Timer 1 oscillator input). Instead, your PCB structure might be simpler if you may move that production to one or the other. For prototyping, usually this doesn't subject both way.
#pragma DATA _CONFIG3H, _CCP2MX_PORTC_3H & _PBADEN_OFF_3H & _MCLRE_ON_3H
CONFIG4L contains some interesting alternatives and shows very clearly how essential it's to have the ability to manage the PIC before startup.
The DEBUG touch allows equipment debugging. You are able to step through code, collection breakpoints and etc - when you yourself have your pc software set precisely and that bit cleared. Equipment debugging also needs the exceptional use of RB6 and RB7 (also employed for ICSP programming). In every honesty, we discover that sequential result is generally sufficient to get bugs, though you are able to debug plenty of PICs with only a PicKit2.
XINST allows for the 18F lengthy training set mode. This isn't utilized by Sourceboost and if you switch it on in error (regardless of the compiler you're using) you will have some pretty unpredictable results. One of our visitors spent times looking for that which was wrong along with his code only to realise the XINST touch was set.
LVP gives you the ability to program the PIC using ICSP without requesting the "higher" Vpp voltage. There is a catch but - you need to devote the RB5 flag (PGM) to becoming an sign if you should be in coding style or not. Given the PicKit2 creates the proper voltage anyway, there doesn't seem to be a lot of price in switching this on for prototyping purposes.
Ultimately, the STVREN offers the choice of having the PIC reset if the stack overflowed or underflowed. If, for example, you contact way too many stacked operates, it would allow the PIC to reset. Once reset, you are able to study why the PIC reset and report a fault. We suggest making this on - if your PIC shoes in the center of doing something, you can fairly assume that you've consumed the stack room (possible when you're strong in a stacked condition and then an stop occurs).
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