PIC Interrupts

1. KONGUNADU COLLEGE OF ENGINEERING &
TECHNOLOGY
(AUTONOMOUS)
20EE807PE – MICROCONTROLLER BASED SYSTEM
DESIGN
UNIT – II
PIC PROGRAMMING AND TIMERS
TAMILNESAN P,
AP/EEE

2. PIC PROGRAMMING AND TIMERS
Instructionset
Addressingmodes
SimpleOperations–Eitherorsequence
Decrementa16bitcounter
Testa16bitvariableforzero
LEDblinksubroutinecode
Codestructureforlargeprograms
Timer0,Timer1
Timer2andprogramming

3. Instruction set
• While writing the instructions the following guidelines are
followed.
• Write the instructions mnemonics in lower case (example:
xorwf)
• Write special Register names, RAM variable names and bit
names in upper case (example: STATUS, RPO….)
• Write instruction and subroutine labels in mixed case
(example: Mainline, LoopTime.)
The instruction set of PIC is divided into three basic categories.
• They are
(a) Byte oriented Instructions
(b) Bit oriented Instructions
(c) Literal and Control Instructions

4. Byte Oriented Instructions
• In a byte oriented Instructions ‘f’ represents a file
register and ‘d’ represents destination register.
• The destination specifies where the result of
operation is to be placed.
• If d = 0, the result is placed in W register
(Accumulator)
• If d = 1, the result is placed in the file register
specified in the instruction.

5. Bit Oriented Instruction
• In bit oriented instructions, ‘b’ represents a bit
field designator which selects the number of
the bit affected by the operation.
• And ‘f’ represents the number of the file in
which the bit is located.

6. Literal and Control Instructions
• In literal and control instructions ‘k’ represents
an 8 or 11 bit constant or literal value.

7. CLASSIFICATION OF INSTRUCTIONS: [Based
on Operation]
• All the instructions of the PIC microcontroller are classified into
nearly 9 groups. They are given below with examples.

11. Addressing modes
The PIC microcontroller supports
• Immediate addressing mode
• Register operand addressing mode
• Memory operand addressing mode
1. Direct Addressing Mode
2. Indirect Addressing mode

12. Immediate addressing mode:
• In this mode, the operand is a number or
constant, not an address as MOVLW43H.
• The operand here is a data not an address.
• So in this addressing mode of PIC
microcontroller data is direct transfer and data
is immediately after opcode.

13. Register operand addressing mode
• In this mode the operand is a register which
holds the data to be execute.
• Register operand addressing mode deals with
registers like W, FSR (File Select Register), INDT
(Indirect Register)

14. Memory Operand addressing mode
• In this mode, the operand is an address of
memory location which holds the data to be
execute.
• The memory operand addressing mode is
classified into,
Direct addressing mode
Indirect addressing mode

15. Direct Addressing Mode
• In direct addressing mode 7 bits (0-6) of the
instruction identify the register file address and the
8th bit of the register file address register bank select
bit (RP0).
• The figure illustrates direct addressing being used to
access register file address 14H or 94H depending on
the value of RP0.
• If the RP0 bit in STATUS register is 0, then the effective
address feeds the 14H in to the Register in the Bank 0.
• If the RP0 bit is 1, then the effective address feeds the
94H in to the register in the Bank 1.

17. Indirect Addressing Mode
• Every instruction that can employ the direct addressing mode
can employ the indirect addressing mode.
• In the indirect addressing mode the full 8-bit register file
address is first written into a File Select Register (FSR) using
direct addressing.
• FSR serves as an address pointer to any address throughout
the entire register file.
• A subsequent direct access of INDF will actually access the
register file using the content of FSR as a pointer to the
desired location of the operand.
• This is possible by making the value of the register bank
select bit RP0, the FSR register is accessed at either address
14H or 94H.
14 H = 00010100 94 H = 10010100