Файл: Basic for PIC Microcontrollers (M. Nebojsa, 2001).pdf

4.5 BRANCHL Jump to the label in second code segment

Variable - Auxiliary variable of byte type (which must be defined at the very beginning of program is used for delay and to repeat the countdown. Before any start of the button instruction it should be initiated on 0.

Action - State at which the jump onto the indicated label is to be effectuated (0 if the button is not pressed, 1 if it is). Simply put, if it is "0" it will jump if the button is not pressed, and if it is 1 it will jump if it is not pressed.

Label - The execution goes on from this label if the Action is correct.

button PORTB.1,0,100,10,B0,1,lab

If the button on pin is pressed, RB1 jumps on the label lab. Button is considered as a pressed on if there is a logical "0" on the RB1 pin.

button PORTB.1,0,100,10,B0,0,lab1

If the button on pin is not pressed, RB1 jumps on label lab1. Button is considered as a pressed on if there is a logical "0" on the RB1 pin.

button PORTB.1,1,100,10,B0,1,lab1

If the button on pin is pressed, RB1 jumps on label lab1. Button is pressed if there is a logical "1" on pin RB1.

Example: The example below will at each pressing of the button, which is connected to RA0, change the state of pin. If the diode is tied to the same pin the effect of the twinkling of the diode will be manifested.

4.7 CALL It calls assemblers subroutine

4.8 CLEAR Sets the value of every variable to 0

Syntax: CLEAR

Description CLEAR sets the entire RAM registers in all databanks to zero. It also means that all the : variables will simultaneously be set to zero.

Example:

4.9 CLEARWDT Resets the watchdog timer

Description Counts the impulses that appear on a specified pin during the time interval defined with : the Period variable. The number of the impulses is stored into the No_Inpulse variable.

Pin is automatically designated as input. Period is specified in milliseconds. If the oscillator is a 4Mhz one, check of a pin state (status) is effectuated every 20 microseconds.

In this way, we can easily measure the frequency of a signal simply by determining number of it's impulses in one second (1000ms). Highest frequency measurable with 4MHz oscillator is 25kHz, while 20MHz oscillator measures up to 125kHz.

Example:

4.11 DATA Effectuates writing into the EEPROM at the first programming

Description DATA stores constants into the internal EEPROM at the first writing of any microcontroller : code. If the initial address from which the storing begins, constants will be stored from

the EEPROM'S zeroth one. Constant may be numerical or character. If it is necessary to save the constant occupying two bytes an official word "word" must be put before that constant (in the adverse case, only the lower byte would be saved.) Instruction DATA is applicable only in those PIC microcontrollers such as PIC16F84 or 16F87X series, which possess the built-in EEPROM memory inside the chip. Apart from the internal EEPROM in PIC microcontrollers exists the option of connecting an additional external EEPROM through the 12C highway. Such mode of connecting in practice in the PIC microcontrollers that don't possess internal EEPROM memory of their own or when its size is inadequate. EEPROM memory has that good property that it doesn't change its value in case of a power shortage. Besides, the possibility of unwanted storing is reduced so that the EEPROM memory is often used to conserve some values of prime importance. For inwriting and reading of EEPROM memories during the operations of microcontroller, instructions WRITE and READ are used.

Example:

4.12 DTMFOUT Generates the tone-dialing signal on the output pin

Description Instruction DTMFOUT produces the tone encountered for example in the phones with tone : dialing. Such characteristic tone is composed of two signals of different frequencies which

serves for the detection of the pressed button. Pin is thereby designated output. The parameter "Onms" represents the duration time of each dial in milliseconds, while "Offms" is the duration of the brake between two consecutive tones. If no value of duration of either tone or brake is set, it goes without saying that "Onms" lasts 200ms and "Offms" 50ms. Tones are numerated 0-15. Those 0-9 are identical to those on a phone dial. Tone 10 represents button * , tone 11 button #, while to the tones 12-15 correspond the additional buttons A-D.

In order to obtain the desired sinusoidal signal at the output, the installation of a sort of filter is required.

Example:

4.13 EEPROM Sets the initial contents for programming EEPROM

: of the location is omitted, the first EEPROM instruction starts to store the constants beginning with an address 0, and the next instructions place the values on the following locations. If the value of location is stipulated, the values are written starting from that very location.

Parameter "Constant" may be number or the sequence of constants. If "word" is not

quoted before constant that is being written in, only the bytes of lowest weights are saved. The sequences of are stored as consecutive bytes of ASCII values.

The instruction "EEPROM" is operative on only those PIC Microcontrollers, which possess EEPROM or FLASH programming memory built in the chip. The date are saved in the EEPROM space when the programming of microcontroller is definitely finished.

For inwriting and reading of EEPROM memory in the course of the operation of the microcontroller, the instructions WRITE and READ are being used.

Example:

4.14 END Marks the logical end of the program

4.15 FREQOUT Generates signal of a specified frequency on output pin