AVR Programming Lesson 7

Questions and Answers

Which of the following is NOT an operand location for an AVR instruction?

Hard Drive (correct)

SRAM

I/O Memory

An AVR instruction can only be one word long.

False

What is the first field of an AVR instruction called?

opcode

The addressing modes of a machine are the various ways used by its instructions to access different _______ that are to be processed.

operands Signup and view all the answers

Match the following AVR addressing modes with their descriptions:

Register Direct = Accesses the operand directly from a register. Immediate Mode = Uses a constant value as the operand. Data Indirect = Accesses operands via a pointer stored in a register. Code Memory Addressing = Accesses the operand from the program memory (Flash). Signup and view all the answers

Which instruction is an example of Relative Program Addressing?

RJMP Signup and view all the answers

The instruction 'IN R25,$16' is classified under Immediate-Register pair Mode.

False Signup and view all the answers

What does the instruction 'ADIW R25:R24, 20' accomplish?

Adds 20 to the contents of registers R25 and R24 combined as a word. Signup and view all the answers

The instruction to load a value directly from data space is called __________.

LDS Signup and view all the answers

Match the addressing modes to their examples:

Indirect Program Addressing = ICALL Data Indirect with Displacement = Rd/Rr q Immediate-Single Register Mode = LDI R16, 78 I/O Direct = OUT $18,R16 Signup and view all the answers

Study Notes

Addressing Modes Overview

Addressing modes define how instructions access operands in a machine.
Instructions sharing the same addressing mode exhibit: consistent length, binary syntax, number of fields, and fetch & execution cycles.

Operand Locations

AVR instruction operands can be located in:
- Register file
- I/O Memory
- SRAM
- Program memory (Flash)

AVR Instruction Format

AVR instructions are either one word (16 bits) or two words (32 bits).
The first field is always the opcode; additional fields (operands) depend on the addressing mode.

Instruction Format Types

Format 1: Opcode only (6 bits).
Format 2: One word (16 bits) or two words (32 bits).
Format 3: One word (16 bits) or two words (32 bits).

AVR Addressing Modes

Register Direct: Involves 1 or 2 registers.
Immediate Mode: Loads immediate values into registers.
I/O Direct: Accesses I/O memory locations directly.
Data Direct: Direct data space access (LDS, STS).
Data Indirect: Accesses data via pointers:
- Pre-decrement mode
- Post-increment mode
Code Memory Addressing: Access to program memory.
Indirect Program Addressing: Includes IJMP and ICALL.
Relative Program Addressing: RJMP and RCALL, where offsets range from -2K to 2K.

Examples of Addressing Modes

Register Direct:
- MOVW R17:R16, R1:R0
Immediate-Single Register Mode:
- LDI R16, 78
- ANI R31, $F0
Immediate-Register Pair Mode:
- ADIW R25:R24, 20
- SBIW R31:R30, $F0
I/O Direct:
- IN R25, $16 (PIN B address)
- OUT $18, R16 (PORT B address)
Data Direct:
- LDS R16, 0x1000
Data Indirect: Uses Rd/Rr options for flexible data referencing.
Program Memory Addressing:
- LPM R3, Z
Indirect Program Addressing Examples:
- IJMP, ICALL
Relative Program Addressing Examples:
- RJMP, RCALL

Assignment Note

Explore the addressing mode for each of the 132 AVR instructions based on the instruction set summary.

Description

Explore the fundamentals of AVR addressing modes and instruction format in this quiz. Learn about the different types of addressing modes and their significance in accessing operands. Perfect for students aiming to deepen their understanding of microcontroller programming.