Gujarat technological university active learning assignment ON ARCHITECTURE OF AVR MICROCONTROLLER at c. K. pithawala college of engineering and technology Prepared by group no. 23 GROUP MEMBERS: TRUPTI BHARGAVE( ) NITESH TIWARI( ) MAHENDRA GUPTA( ) RAHUL SINGH( ) VISHAL GUDLA( )

AVR Microcontroller AVR stands for? Advanced Virtual RISC, The founders are Alf Egil, Bogen Vegard Wollan RISC. AVR architecture was conceived by two students at Norwegian Institute of Technology (NTH)[1] and further refined and developed at Atmel Norway, the Atmel company founded by the two chip architects.

AVR Architecture I

Harvard Architecture  In a Harvard architecture, there is no need to make the two memories share characteristics. In particular, the word width, timing, implementation technology, and memory address structure can differ. In some systems, instructions can be stored in read-only memory while data memory generally requires read-write memory. In some systems, there is much more instruction memory than data memory so instruction addresses are wider than data addresses.wordmemory addressread-only memoryread-write memory Howard Hathaway Aiken  The Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data.computer architecturestorage  The term originated from the Harvard Mark I relay- based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters.Harvard Mark Ipunched tape

The Harvard Architecture Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters (23 digits wide). These early machines had limited data storage, entirely contained within the data processing unit, and provided no access to the instruction storage as data, making loading and modifying programs an entirely offline process.

The Harvard Architecture Slide 6 In a computer with a von Neumann architecture (and no cache), the CPU can be either reading an instruction or reading/writing data from/to the memory. Both cannot occur at the same time since the instructions and data use the same bus system. In a computer using the Harvard architecture, the CPU can read both an instruction and perform a data memory access at the same time, even without a cache. A Harvard architecture computer can thus be faster for a given circuit complexity because instruction fetches and data access do not contend for a single memory pathway.

The Harvard Architecture Slide 7 In a Harvard architecture, there is no need to make the two memories share characteristics. In particular, the word width, timing, implementation technology, and memory address structure can differ. In some systems, instructions can be stored in read-only memory while data memory generally requires read-write memory. Instruction memory is often wider than data memory.

Harvard architecture 8 CPU PC data memory program memory address data address data

Harvard Architecture Example Slide 9 Block Diagram of the PIC16C8X

Modified Harvard Architecture Slide 10 The Modified Harvard architecture is very like the Harvard architecture but provides a pathway between the instruction memory and the CPU that allows words from the instruction memory to be treated as read-only data. This allows constant data, particularly text strings, to be accessed without first having to be copied into data memory, thus preserving more data memory for read/write variables. Special machine language instructions are provided to read data from the instruction memory. Standards-based high-level languages, such as the C language, do not support the Modified Harvard Architecture, so that in-line assembly or non-standard extensions are needed to take advantage of it. Most modern computers that are documented as Harvard Architecture are, in fact, Modified Harvard Architecture.

Modified Harvard Architecture A modified Harvard architecture machine is very much like a Harvard architecture machine, but it relaxes the strict separation between instruction and data while still letting the CPU concurrently access two (or more) memory buses. The most common modification includes: Separate instruction and data caches backed by a common address space. While the CPU executes from cache, it acts as a pure Harvard machine. When accessing backing memory, it acts like a von Neumann machine (where code can be moved around like data, a powerful technique). This modification is widespread in modern processors such as the ARM architecture and X86 processors.cachesARM architectureX86 Provides a pathway between the instruction memory (such as ROM or flash) and the CPU to allow words from the instruction memory to be treated as read-only data. This technique is used in some microcontrollers, including the Atmel AVR. This allows constant data, such as text strings or function tables, to be accessed without first having to be copied into data memory, preserving scarce (and power-hungry) data memory for read/write variables. Special machine language instructions are provided to read data from the instruction memory. (This is distinct from instructions which themselves embed constant data, although for individual constants the two mechanisms can substitute for each other.)Atmel AVR

Von Neumann Architecture  The phrase Von Neumann architecture derives name of the mathematician and early computer scientist John von Neumann.mathematician computer scientistJohn von Neumann  The meaning of the phrase has evolved to mean a stored-program computer in which an instruction fetch and a data operation cannot occur at the same time because they share a common bus. This is referred to as the Von Neumann bottleneck and often limits the performance of the system.busVon Neumann bottleneck John von Neumann  In contrast with the Harvard architecture, the Von Neumann architecture has a single storage structure to hold both instructions and data. The CPU can be either reading an instruction or reading/writing data from/to the memory because instructions and data use the same bus system.

The Von Neumann Architecture 13 Model for designing and building computers, based on the following three characteristics: 1) The computer consists of four main sub-systems: Memory ALU (Arithmetic/Logic Unit) Control Unit Input / Output System (I/O) 2) Program is stored in memory during execution. 3) Program instructions are executed sequentially.

The Von Neumann Architecture Memory Processor (CPU) Input-Output Control Unit ALU Store data and program Execute program Do arithmetic/logic operations requested by program Communicate with "outside world", e.g. Screen Screen Keyboard Keyboard Storage devices Storage devices Bus

von Neumann architecture 15 Memory holds data, instructions. Central processing unit (CPU) fetches instructions from memory. Separate CPU and memory distinguishes programmable computer. CPU registers help out: program counter (PC), instruction register (IR), general-purpose registers, etc.

The von Neumann model Slide 16 InputOutput So where is the Input/Output? here CPU Buses

von Neumann vs. Harvard 17 Harvard can’t use self-modifying code. Harvard allows two simultaneous memory fetches. Most DSPs use Harvard architecture for streaming data: greater memory bandwidth; more predictable bandwidth.

18