• RA0 (pin 19), RA1 (pin 20), RA2 (pin 1), RA3 (pin 2), T0CKI/RA4 (pin 3): These pins belong to Port A, which is a 5-bit bi-directional I/O port. The pins RA0 to RA4 can be used for digital input or output. T0CKI is the Timer0 external clock input, which can be used for external event counting or for timing applications when configured in timer mode.
• MCLR (pin 4): This is the Master Clear (reset) input. By applying a logical low level to this pin, you can reset the microcontroller, clearing the program counter and resetting most of the registers to their default state. In many applications, this pin is connected to a push-button switch to hardware reset the microcontroller, usually with a pull-up resistor to VDD.
• VSS (pin 5 and 6): These are the ground (0V) pins of the microcontroller. They need to be connected to the ground plane of your PCB or to the negative terminal of your power supply.
• INT/RB0 (pin 7), RB1 (pin 8), RB2 (pin 9), RB3 (pin 10), RB4 (pin 11), RB5 (pin 12), RB6 (pin 13), RB7 (pin 14): These pins are part of Port B, which is an 8-bit bi-directional I/O port with interrupt-on-change capability. The INT/RB0 pin can also be used as an external interrupt input pin.
• VDD (pin 15 and 16): These are the power supply pins for the microcontroller. This is where you supply the operational voltage to the microcontroller, which is typically +5V for the PIC16F84A.
• OSC2/CLKOUT (pin 17), OSC1/CLKIN (pin 18): These are the oscillator pins. OSC1 is the input to the oscillator, and OSC2 outputs the oscillator frequency, which can be used to clock other devices. You can use these pins with an external crystal oscillator, ceramic resonator, or an external clock source to provide a clock for the microcontroller's operations.

1. Timing Basis: The oscillator generates a continuous, stable clock signal that serves as the heartbeat for the microcontroller. This clock signal determines the speed at which the microcontroller operates, ensuring that instructions are executed at a consistent rate. Essentially, each pulse of the clock signal allows the microcontroller to execute a portion of its program, so without an oscillator, the microcontroller would not be able to process instructions.
2. Peripheral Synchronization: Many of the microcontroller's peripherals (e.g., timers, communication interfaces) need a clock signal for their operation. The oscillator ensures that these components work in sync with the core processing unit, enabling functionalities like timed events, serial data communication, and PWM (Pulse Width Modulation) output.
3. Determining Operation Speed: The frequency of the oscillator dictates the microcontroller's operating speed. For the PIC16F84A-20I/SS, the oscillator frequency impacts how quickly it can execute instructions. A higher frequency means faster execution of the program but also higher power consumption. This allows designers to balance between performance and power efficiency based on the application's needs.
4. Flexibility and Precision: Different applications require different timing precision and system speeds. By selecting an appropriate oscillator (crystal, ceramic resonator, or external clock), designers can tailor the system performance to the application’s requirements. Crystals, for instance, offer high precision and stability, making them suitable for time-critical applications.
5. External Synchronization: In some applications, microcontrollers need to operate in sync with other microcontrollers or external devices. An oscillator can be used to ensure that the system works in harmony with an external clock source, maintaining synchronized operation across devices.

• Type: Flash
• Size: 1K x 14 bits

• General Purpose Registers (GPR):
  • These are used for temporarily storing data during program execution. GPRs are used for variable storage, intermediate calculations, and controlling the flow of the program.
• Special Function Registers (SFR):
  • SFRs are used to control and monitor the operation of the microcontroller’s peripherals, such as ports (e.g., PORTA and PORTB), timers, and the program counter. SFRs include registers that control I/O pin directions (TRISA and TRISB for controlling the direction of PORTA and PORTB pins), and others that control operation modes of various internal peripherals.
• Size: 68 x 8 bits

• Type: EEPROM
• Size: 64 x 8 bits

• The W register is an 8-bit register that acts as the primary accumulator for arithmetic and logic operations. Think of it as a general-purpose register that's used almost like a temporary storage space for data that's being worked on.
• When you perform an operation (be it arithmetic like addition or subtraction, or logical like AND, OR, NOT), the result can be stored in the W register.
• Many instructions involve the W register implicitly or explicitly. For example, an ADDLW instruction adds a literal value (a constant embedded in the instruction code) to the contents of the W register and stores the result back in the W register.

• The term F register doesn't refer to a single register, but rather to any register within the data memory (which includes both the General Purpose Register (GPR) area and the Special Function Registers (SFR) area). Hence, an F register is often mentioned in the context of operations that involve reading from or writing to a specific register in the data memory.
• Each F register has a specific address that's used to access it. These registers can hold data that your program will manipulate or they can be SFRs which control the microcontroller's peripherals (like setting a port pin to be an input or an output).
• Instructions that involve F registers typically allow you to specify whether the result of the operation should be stored in the W register or back into the F register itself. This is where you'll encounter the d operand in instruction syntax, where d=0 means the result is stored in the W register, and d=1 means it's stored back in the F register.

• Download and Install MPLAB X IDE: You can get MPLAB X from Microchip's official website. It's the software where you'll write your code, compile it, and upload it to your PIC microcontroller.
• Download and Install a Compiler: For PIC16F84A, you'll primarily use the MPLAB XC8 compiler for C programming or an assembler for assembly programming. Ensure you download and install an appropriate compiler compatible with MPLAB X IDE.

• Open MPLAB X IDE and select "Create New Project" from the File menu.
• Choose a "Standalone Project" and select the PIC16F84A microcontroller from the list of devices.
• Select the toolchain to use (MPLAB XC8 Compiler for C or the MPASM assembler for assembly projects).
• Choose a project name and location to save it.

• Start with a Template or Empty File: MPLAB X IDE might offer you a template when creating a new file. For absolute beginners, starting with an example or template can be helpful.
• Writing Code: If you're using the C language, your program will start with a main function, which is the entry point of your application. If you're writing in assembly, you start with an initialization section followed by your main loop.

C
#include 

// Configuration bits (specific for PIC16F84A)

void main() {
    TRISB = 0; // Configure all PORTB pins as output
    while(1) { // Infinite loop
        PORTB = 0xFF; // Turn on all LEDs connected to PORTB
        _delay(500000); // Delay
        PORTB = 0x00; // Turn off all LEDs
        _delay(500000); // Delay
    }
}

• Compile Your Code: Use the "Build Project" button (usually an icon with a hammer) in MPLAB X IDE. If there are no errors, the IDE will create a .hex file, which is the binary file to be uploaded to the microcontroller.

• Use a PIC Programmer: To upload the compiled program (.hex file) to your PIC16F84A, you'll need a hardware programmer (such as PICkit 3 or 4, depending on availability). Connect your programmer to your computer and to the PIC16F84A on your circuit.
• Write the Program: Using MPLAB X IDE, select the option to "Make and Program Device". This action will transfer the .hex file to your PIC16F84A.

Assembly
    LIST p=16F84A       ; Tell assembler what chip we are using
    include "p16F84A.inc" ; Include the definitions for this chip
    __CONFIG _CP_OFF & _WDT_OFF & _PWRTE_ON & _XT_OSC ; Configuration bits

    ORG 0x00            ; Start at address 0
    goto INIT           ; Jump to initialization routine

MAIN_LOOP
    movlw 0xFF          ; Load W register with 0xFF (all LEDs ON)
    movwf PORTB         ; Move W register value to PORTB
    call DELAY          ; Call delay
    movlw 0x00          ; Load W register with 0x00 (all LEDs OFF)
    movwf PORTB         ; Move W register value to PORTB
    call DELAY          ; Call delay
    goto MAIN_LOOP      ; Repeat the loop

INIT
    bsf STATUS,RP0      ; Switch to Bank1 to access TRIS registers
    movlw 0x00          ; Set all PORTB pins to output
    movwf TRISB         ; Move the value to the TRISB register
    bcf STATUS,RP0      ; Switch back to Bank0
    goto MAIN_LOOP      ; Go to the main loop

DELAY
    movlw 0xFF          ; Set up outer loop counter
    movwf COUNT1
OUTER_LOOP
    movlw 0xFF          ; Set up inner loop counter
    movwf COUNT2
INNER_LOOP
    decfsz COUNT2,F     ; Decrement COUNT2, skip next if 0
    goto INNER_LOOP     ; Repeat inner loop until COUNT2 is 0
    decfsz COUNT1,F     ; Decrement COUNT1, skip next if 0
    goto OUTER_LOOP     ; Repeat outer loop until COUNT1 is 0
    return              ; Return from delay

    END                 ; End of program

• I/O Configuration: Sets the direction (input or output) of the GPIO pins. For example, configuring PORTB pins as outputs to drive LEDs.
• Peripheral Setup: Configures the microcontroller's peripherals according to the application's needs, such as timers, serial communication settings, analog to digital converters, etc.
• Program Setup: Initializes program variables or flags that control the flow of the program. For example, setting initial values or clearing flags.
• Clock Configuration: In some microcontrollers, you might need to configure the clock source or prescaler options during initialization to ensure the system operates at the intended frequency.

• movlw: This is the mnemonic for "MOVe Literal to W-register." It's an instruction that loads a specified immediate value (a literal) directly into the W register. The W register is the Working register, a general-purpose register used for arithmetic and logic operations in the PIC microcontroller.
• 0x00: This specifies the literal value to be loaded into the W register. The prefix 0x indicates that the number that follows is represented in hexadecimal (base 16) notation. A value of 00 in hexadecimal is equivalent to 0 in decimal. Essentially, this part of the instruction sets the value to zero.

• Compactness: Hexadecimal notation is more compact than decimal for representing large numbers, which is particularly useful in the context of programming and memory addresses.
• Clarity: Using hexadecimal makes it clearer that you're dealing with values that might directly correspond to binary representations or memory addresses, providing insight into the operation's effect at the bit level.
• Convention: It’s a common convention in embedded systems and low-level programming to use hexadecimal notation, as it aligns well with the inherent base-2 operations of digital electronics.

• Bank 0: This is the default bank that the microcontroller starts in after a reset. It contains the first set of Special Function Registers (SFRs) and General Purpose Registers. Operations that deal with core functionalities, like manipulating I/O ports directly or working with timer settings, often use registers in Bank 0.
• Bank 1: This bank also contains SFRs and GPRs, but the SFRs in Bank 1 are typically used for more specific configurations, such as setting the I/O direction (making a pin an input or an output) using TRIS registers. The registers in Bank 1 are not directly accessible without first switching from Bank 0.

• To access Bank 1, you set the RP0 bit to 1.
• To return to Bank 0, you clear the RP0 bit to 0.

1. Switch to Bank 1 by setting the RP0 bit in the STATUS register.
2. Write 0x00 to the TRISB register, configuring all PORTB pins as output. (0 means output, 1 means input).
3. Switch back to Bank 0 to perform regular operations, such as writing to or reading from PORTB.

Assembly
bsf STATUS,RP0      ; Switch to Bank1 (Bit Set File: set RP0 bit in STATUS register)
movlw 0x00          ; Set all PORTB pins to output (0 means output)
movwf TRISB         ; Move the literal value to the TRISB register
bcf STATUS,RP0      ; Switch back to Bank0 (Bit Clear File: clear RP0 bit in STATUS)