2. Why are there two GND-pin which are internally shorted (I measured practically).
3. Do you suggect to include a fast switching diode at the RESET circuit (Fig-1, post #36) for the suppression of the transient voltage dveloped by C1 while being shorted to GND?
4. Do you suggest to add a 100 ohm resistor in series with the RST swicth to lower the discharge current of C1 (Fig-1 of post #36)?
5. Is it good to short AVCC with VCC or leave it isolated so that an external L-C filter could be added in a noisy environment?
I'm recommending to read AVR042: AVR Hardware Design Considerations.
I think the best RESET circuit has definitely UNO R3, also Mega R3. There is 10k pull-up with parallel backward diode (not zenner, why?), eventually 100nF to an external reset pulse (typically DTR or RTS signal).
The RESET pin has an internal low-pass filter so no capacitor is needed (between RESET and GND). 10uF is really too much and if so then small resistor in series with RST switch will limit the discharging current. It is never good idea to discharge the capacitor with shortage. This will cause the capacitor to wear out quickly or even damage it. Besides, the current pulse can damage other parts close to place of discharge.
Good design should have connected all power pins and to have them decoupled like @groundFungus wrote in #34. Decoupling capacitors as close as possible to the pins, extra for each one. All GND pins together (of course, they are connected internally).
Normally, VCC and AVCC can be connected. There is a recommendation for noisy environment to leave them separately with filter on AVCC.
Why are there two GND-pin which are internally shorted (I measured practically).
The GND pins on the controller spreads the ground current path to 2 pins. You get some isolation benefits of reduced noise between digital and analog signals.
Do you suggect to include a fast switching diode at the RESET circuit (Fig-1, post #36) for the suppression of the transient voltage dveloped by C1 while being shorted to GND?
Best practices place this diode so you get a fast discharge path for the capacitor at power down.
Do you suggest to add a 100 ohm resistor in series with the RST swicth to lower the discharge current of C1 (Fig-1 of post #36)?
Probably not needed, however, it lengths the discharge time or reset time on a press of the reset switch which might be an advantage in some conditions.
Is it good to short AVCC with VCC or leave it isolated so that an external L-C filter could be added in a noisy environment?
If supply and digital switching noise needs to be filtered for the analog inputs, keep these pins separated with AVCC having the filter network that you are describing.
Thanks for one-to-one analysis and answer. I have been highly benefitted and educated from post #46@Budvar10 and post #49@LarryD in respect of the optimum design of the external RESET circuit of ATmega328P MCU.
All done now. Found the connections to the atmega328 on Autodesk Instructables. Article called âbare minimum Arduino on breadboardâ. Even explains how to burn bootloader on chip if it doesnât already have one. Apparently some Atmega have a bootloader already installed and some donât.
Is the bootloader a short program that converts the downloaded Arduino program to machine code?
Please, give a search to the net; you will find many write-ups on Bootloader Program. Read them, summarize your understandings, and then post it. There are good teachers in the Forum who will be kind to refine your post.
Also the act of bootloading can set fuses in the chip that select options like clock source, clock frequency, brown out reset level, watch dog timer and others.
For instance, when I bootload tiny85 processors I usually do not install the bootloader code, I only set fuses.
No. You can upload program ATmega via ISP by default (also with parallel programming but it is more complicated). The bootloader is needed to do the same thing via serial line.
Apparently some Atmega have a bootloader already installed and some donât.
Factory default is without the bootloader or any other program. It is just raw chip.
What is a Bootloader Program? 1. The Flash Memory of ATmega328P MCU of Arduino UNO Board has been divided into three sections (Fig-1): (1) Interrupt Vector Flash Section, (2) Application Flash Section, and (3) Boot Flash Section.
2. The Binary Codes/Machine Codes of the application program (user sketch) is stored in the Application Section.
3. These are the steps being carried out by the user and Arduino IDE to store the binary codes of the user sketch into the application section. (1) The user creates his sketch using Arduino IDE. For example: To show the message "Hello" on the Serial Monitor.
(2) When the Compile Button is clicked, the high level sketch is converted into binary codes (machine codes). The binary codes are then converted into many frames of Intel-Hex format type which are suitable to transmit from PC to Aduino UNO Board using Serial Port. For example: The sketch of Step-3(1) has been converted into 94 hex-formatted frames from which I am showing below the first one and the last two:
:10 0000 00 0C9435000C945D000C945D000C945D00 24 (spaces are shown for clarity)
.........................
:0C05BC00AF0048656C6C6F000D0A000079
:00 0000 01 FF (this frame contains the end-of-file message (01))
(3) The 1st frame of the above three contains the following prtial binary codes of the sketch, which will be stored in the application section:
0C94 3500 0C94 5D00 0C94 5D00 0C94 5D00 (spces are shown for clarity)
(4) The Boot Section of Fig-1 holds a small program called Bootloader Programmer which is pre-installed by Arduino. The Bootloader Program receives the Hex-formatted frame of Step-3(2) from PC, extracts the binary codes (machine codes) of Step-3(3) and then stores them into the application section using SPM (Store (into) Program Memory) instruction. The process continues until all the Inte-Hex frames are received and the binary codes of the full sketch is stored in the application flash.
(5) Once storing/loading of the binary codes is done, the control goes to location 0x0000 (Fig-1) and then control goes to the beginning address (0x0035 as is found in this opcode: 0000 - 0C943500; jmp 0x0035 of the 1st frame) of the loaded application program to begin the execution of the sketch.
Or you can disable reset (mostly done on ATtiny chips/boards) and cycle power to reset.
An AVR needs only MCU, power, ground, 2 bypass caps, a program and some kind of IO to show that IT'S ALIVE! Igor! The schnapps!
Nick Gammons tutorial linked in the post between 1 and 2.. even if you never build one with teach a whole lot about making stand-alone end-products powered by AVRs. He shows 2 but there are many others with the same core with different resorces/features.
I follow these steps to develop my stand-alone hobby system using 328P MCU: 1. I use a suitable AVR Programmer to erase the chip. 2. Record the Fuse Bits. 3. Set the Fuse Bits for:
4. Develop sketch using Assembler and Arduino IDE. 5. Store the skech (Intel-Hex Format) using AVR Programmer. 6. Place the MCU on the Breadbord. 7. Connect the components and power supply as needed. 8. Observe the output on display unit (LED, 7-sement, LCD).
