Arduino (ATmega328/p) Architecture Explained

Arduino: The name Arduino comes from a bar in Ivrea, Italy, where some of the founders of the project used to meet. The bar was named after Arduin of Ivrea, who was the margrave (Military Commander)of the March of Ivrea and King of Italy from 1002 to 1014.

Today, Arduino is an open source computer hardware and software company, project and user community that designs and manufactures single-board microcontrollers and microcontroller kits for building digital devices and interactive objects that can sense and control objects in the physical and digital world.

Arduino board designs use a variety of microprocessors and controllers. The boards are equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields) or Breadboards (other circuits on them).

Arduino Uno is a microcontroller board based on the ATmega328P (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz crystal, a USB connection, a power jack, an ICSP header and a reset button. It contains everything needed to support the microcontroller, simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. You can tinker with your UNO without worrying too much about doing something wrong, worst case scenario you can replace the chip for a few dollars and start over again.

“Uno” means one in Italian and was chosen to mark the release of Arduino Software (IDE) 1.0. The Uno board and version 1.0 of Arduino Software (IDE) were the reference versions of Arduino, now evolved to newer releases. The Uno board is the first in a series of USB Arduino boards, and the reference model for the Arduino platform. (IDE = integrated development environment)

The input voltage (7 – 12 V) to the Arduino board when it’s using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through the Vin pin, or, if supplying voltage via the power jack, access it directly through Vin pin.

Architecture: means the complex or carefully designed structure of something.

Here Architecture is of Arduino or precisely the IC of Arduino (ATmega328p). The  ATmega328/P is a low-power CMOS 8-bit microcontroller based on the AVR® enhanced RISC (reduced instruction set computer) architecture.
In Order to maximize performance and parallelism, the AVR uses Harvard architecture – with separate memories and buses for program and data. Instruction in the program memory are executed  with a single level of pipelining.
The clock is controlled by an external 16MHz Crystal Oscillator.

The basic working of  CPU of  ATmega328:-
1. The data is uploaded in serial via the port (being uploaded from the computer’s Arduino IDE). The data is decoded and then the instructions are sent to instruction register and it decodes the instructions on the same clock pulse.
2. On the next clock pulse the next set of instructions are loaded in instruction register.
3. In general purpose registers the registers are of 8-bit but there are 3 16-bit registers also.
a. 8-bit registers are used to store data for normal calculations and results.
b. 16-bit registers are used to store data of timer counter in 2 different register. Eg. X-low & X-high. They are fast, and are used to store specific hardware functions.
4. EEPROM stores data permanently even if the power is cut out. Programming inside a EEPROM  is slow.
5. Interrupt Unit checks whether there is an interrupt for the execution of instruction to be executed in ISR (Interrupt Service Routine).
6. Serial Peripheral Interface (SPI) is an interface bus commonly used to send data between microcontrollers and small peripherals such as Camera, Display, SD cards, etc. It uses separate clock and data lines, along with a select line to choose the device you wish to talk to.
7.Watchdog timer is used to detect and recover from MCU malfunctioning.
8. Analog comparator compares the input values on the positive and negative pin, when the value of positive pin is higher the output is set.
9. Status and control is used to control the flow of execution of commands by checking other blocks inside the CPU at regular intervals.
10. ALU (Arithmetic and Logical unit)The high performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a single clock cycle, arithmetic operations b/w general purpose registers are executed. The ALU operations are divided into 3 main categories – arithmetic, logical and bit-function.
11. I/O pins The digital inputs and outputs (digital I/O) on the Arduino are what allow you to connect the Arduino sensors, actuators, and other ICs. Learning how to use them will allow you to use the Arduino to do some really useful things, such as reading switch inputs, lighting indicators, and controlling relay outputs.

EXTRA:
1.Automatic (Software) Reset:
 Rather then requiring a physical press of the reset button before an upload, the Arduino is designed in a way that allows it to be reset by software running on a connected computer. The Arduino Software (IDE) uses this capability to allow you to upload code by simply pressing the upload button in the Arduino environment. This means that the bootloader can have a shorter timeout, as the lowering of DTR (Data Terminal Ready) can be well-coordinated with the start of the upload.

2.Firmware: Firmware is a software program or set of instructions programmed on a hardware device. It provides the necessary instructions for how the device communicates with the other computer hardware. Firmware is held in non-volatile memory devices such as ROM.

3.To check whether the firmware is installed in your Arduino or not just press the reset button and if the inbuilt LED flickers (on pin 13) the firmware is present.

References:
A. Arduino.cc
B. Wikipedia.com
C. Datasheet of ATmega328/p

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