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Topic: Standalone Atmega328p-au (Read 2038 times) previous topic - next topic


Dear all,

I have been reading about the atmega328 family and now I am more confused about this than before.

I will be using a standalone atmega328p-au, where p stands for picopower (less power consumption), and au stands for tqfp. I hope I am correct so far?

I need to burn the arduino bootloader on the blank chip, because I need to be able to upload the code whenever necessary. Once the bootloader is burnt on the chip I will only have (direct) access to Rx, Tx, Vcc, Vgnd and RST pins.

I need some advice on how to burn the bootloader (and upload sketches) using this method: http://arduino.cc/en/Tutorial/ArduinoToBreadboard.

Since the Uno atmega328p-pu (28 pins) is different from atmega328p-au (32 pins), will it be possible to use the optiboot bootloader? Do the two chips have different signatures? Arduino Nano v3.0 has the same chip I will be using. So I can just select Arduino Nano board to burn the bootloader using the same method?

I have seen some vague answers on this topic, but did not find any straightforward answer.

Thank you for your help and best regards,


Apr 16, 2013, 04:02 pm Last Edit: Apr 16, 2013, 04:18 pm by Chimera Reason: 1
I am attaching the relevant schematics.

Can I use Arduino Nano (atmega328p-au) first to burn the bootloader to a blank atmega328p-au using the VCC, GND, MISO, MOSI, SCK and SS (to RESET) pin and then use a FTDI adapter to program the bootloaded chip using the TX, RX, RESET, VCC and GND pins? Is the schematic diagram correct, since I did not use a capacitor on the reset?

Best regards,


Schematic is correct, altho incomplete.
Add 0.1uF from reset to DTR for software reset during serial download.
Add 0.1uF from VCC to Gnd.
Add 0.1uF form AVcc to Gnd.
Doing any analog inputs? Add 0.1uF from Aref to Gnd.

Otherwise, looks good for programming bootloader via ICSP pins (SCK, MISO, MOSI, Reset, Vcc, GND)
and then serial downloads vis Rx, Tx, DTR, +Vcc, GND.

VCC will connect to 5V?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Apr 17, 2013, 08:42 am Last Edit: Apr 17, 2013, 08:45 am by Chimera Reason: 1
Dear CrossRoads,

thank you very much for the answer. I modified my wiring sketch (attachment) according to your advice. Is this correct now? I will include ICSP header with MISO, MOSI, RESET, SCK, VCC and GND (as shown in the wiring sketch). And after burning the bootloader (I was thinking of buying AVRISP mkII), I can upload sketches via a FTDI using VCC, GND, RX, TX and DTR. The difference between DTR (software reset) and RESET is only the 0.1 uF capacitor?

I am using only 3 PWM outputs and I2C lines (SDA, SCL). Do I need AREF wired in this case? The same two pins are also used for analog input (but are in my case configured as I2C).

Thank you again,

P.S.: Yes, VCC is 5V.

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