PIC18 Microcontroller Architecture and Programming Fundamentals

1. PIC18 Architecture Details

• Harvard Architecture

  Features distinct program memory and data memory. Includes the MPU, Program Memory, Data Memory, I/O Ports, and support devices like timers.

• Microprocessor Unit (MPU)

  • ALU (Arithmetic Logic Unit)

    Performs operations such as addition, subtraction, and logical operations.

  • Registers

    Includes WREG (8-bit accumulator), Program Counter (PC), Stack Pointer (SP), and File Select Registers (FSRs).

  • Memory

    Offers 2 MB of program memory and 4 KB of data memory.

  • Bank Switching

    Data memory is divided into 16 banks, with one 256-byte access bank.

2. Data Formats and Representations

• Unsigned Integers

  These are 8-bit values, ranging from 0 to 255.

• Signed Integers

  Represented using 2's complement, with a range from -128 to 127.

• BCD (Binary Coded Decimal)

  Each byte is split into two 4-bit nibbles, representing decimal digits 0 through 9.

• ASCII

  A 7-bit alphanumeric code, with values ranging from 0x00 to 0x7F.

3. PIC18 Registers and Memory

• Special Function Registers (SFRs)

  These control the CPU and peripherals. Examples include PORTx (for I/O ports), TMRx (timers), and STATUS (arithmetic status).

• General Purpose Registers (GPRs)

  Used primarily for variable storage during program execution.

4. Assembly Language Programming

• Basic Instructions

  Key instructions include MOV, ADD, SUB, AND, OR, XOR, NOP, and GOTO.

• Control Flow

  Control flow is managed using:

  • GOTO (long jump)
  • BRA (short jump)
  • CALL and RETURN for subroutine handling.

• Flags

  Flags used in arithmetic and logical operations include N (Negative), Z (Zero), C (Carry), OV (Overflow), and DC (Digit Carry).

5. Timers, Interrupts, and I/O Ports

• I/O Ports

  Controlled by the PORTx and TRISx registers, allowing pins to be configured as input or output.

• Timers

  The PIC18 features multiple timers, such as Timer0 and Timer1, for time-based operations.

• Interrupt Handling

  Interrupts can be configured to trigger on specific conditions, such as timer overflows or external events.

6. Peripheral Interfacing

• LED and 7-Segment Displays

  Interfacing involves setting I/O pins, often requiring multiplexing for multiple digits.

• Keypad Interface

  This typically involves scanning rows and columns to detect keypresses.