Help with Serial Communications

Discussion in 'Embedded Systems and Microcontrollers' started by OmnipotentTech, Apr 12, 2011.

  1. OmnipotentTech

    Thread Starter New Member

    Apr 12, 2011
    Ok, This will be my first post.
    I am having trouble understanding the difference between RS-232 and USB communications. Specifically, I am having trouble understanding how to wire them for communications with an ATmega microcontroller.
    So Heres where I am, I am thinking I can Wire my USB port on my computer as follows
    Pin 1 USB to ATmega8 Pin 31 UVCC
    Pin 2 USB to ATmega8 Pin 30 D-
    Pin 3 USB to ATmega8 Pin 29 D+
    Pin 4 USB to ATmega8 Pin 28 UGND
    You can see this in a schematic at:

    So that being said, Will this cause any problems? The ARDUINO website has a MINI USB adapter board, its page says; "Mini USB Adapter-This board converts a USB connection into 5 volt TX and RX that you can connect straight to the Arduino Mini or other microcontrollers, allowing them to talk to the computer. It is based on the FT232RL chip from FTDI."

    From what I can tell, the ARDUINO Uno board wires its USB connection into an arbitrary ATmega8 and then wires its I/O pins to an ATmega32.

    Do USB Com ports run at 3.3 volts?
    Do Serial Ports run at 5 volts?
    Cant i just use an operational amplifier in line with my USB To program my AVR?
    Does the ATmega series of ICs only read and write binary at 5 volts?
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    What AVR are you using?

    Are you using the ATMega 328 or an Arduino? or some other AVR?

    What are you using to program it?

    If you are trying to use the usb port directly to program it, it will not work.

    The AVR operates at 5v (or 3.3v) but requires higher voltages to program.
  3. OmnipotentTech

    Thread Starter New Member

    Apr 12, 2011
    I will be using the ATmega328P-PU
    im sort of creating my own "on proto board" Arduino for a project
    I will be using the Arduino enviroment to program my microcontroller

    I was planning on wiring a ATMEGA8U2-MU as i explained earlier
    then connecting that to a ATMEGA328P-PU
    the pin diagram would be like this
    Atmega8 pin 9 to Atmega32 pin 2
    Atmega8 pin 8 to Atmega32 pin 3
    you can see this here:

    could I just use wire a serial port in the same way as i purposed for the USB?

    or do i need some sort of Bootloader IC?

    Like a MAX232?
  4. eblc1388

    Senior Member

    Nov 28, 2008
    Exactly how high the voltage be?