SERIAL to USB Home Made Using ATmega8

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the other choice build your own USB to Serial whitout microcontroller clik THIS 

In the following article will discuss how to implement and make a USB to Serial Converter own with ATmega8 microcontroller. In this ATmega8 will be given free firmware source code and can be downloaded at the bottom.

Because the ATmega8 there is no facility for communication with the USB, then inevitably the data with the USB communication protocol must be made on the firmware itself. For a study guide the USB protocol can be seen in other parts of this website or click the link below to view it. In the firmware can be downloaded existing code to handle USB protocol, so that can be directly used, but if you want to add another facility, you can edit the firmware. The firmware provided is written in assembler language that can be done and compiled with AVR Studio 4. In addition to code Assemblernya also included his Hexa code compilation results of AVR Studio 4 which can be directly entered in his IC.

Here is a circuit schematic drawing USB to Serial converter with ATmega8.USB data line of D + and D-connected to PB0 and PB1 in the ATmega8, this connection should not be changed because of these pins can be done with high-speed data transfer. For there was a connection and the opinion of a good signal between USB and devices, then ATmega8 be hired at Low Speed ​​data rate that is the way her pull-up 1k5 Ohm resistor on the D-line data. For the other components are only used as a complement for the system to beropersai with good, for example Xtall used as a clock and used as a filter capacitor power supply.

If at this circuit you want a USB to RS-232 converter then you need to add the IC MAX 232 as Level converter from TTL to RS232 levels. If you only want to use to control the LED you can directly connect to the PIN I / O directly in series with a resistor before.

For the implementation of the firmware as the USB receiver and coding of protocolnya, will receive all the packets of data from USB and then stored in an internal buffer. Starting from the first revenues derived from external interrupt (INT0) is the data to "sync pattern", during the admissions process only the last packet in the check the signal EOP (End of Packet). After the admissions process successfully, the next firmware will mong-coding a number of data packets it receives and then analyze it. Once again because of the USB protocol is very difficult you can read again the USB protocol on the following links. The process of receiving data on a USB in general can be seen in the following flowchart flow.Firmware is generally divided into several sections main blocks, namely:

* Interrupt Routine
* Decoding Routine (Includes NRZI Encoding, BitStuffing Removal / Addition).
* USB Reception
* USB Transmission
* Requested Action Decoding
* Performing Custom Actions Requested

Users can add the function of certain functions into the firmware, like the function to create a "Customer-Specific", function to "Direct Pin Control" and so forth. To complete the firmware can be downloaded at the bottom.

For ATmega8 that will be used the following support for 800-byte FIFO buffer, with baudrate baudrate 300 to 115 200, databit (5,6,7,8), stopbit (1.2), and its parity (none, odd, even, mark , space).

By using this ATmega8 there are some possible features that can be added for example:

* USB read / write to internal memory that is 512 byte EEPROM to store data such as calibration data or data product code.
* Possibility to use PWM and ADC (Analog to Digital Converter) which is in ATmega8.
* With the program memory space that is still large, the user can add other facilities such as for USB to I2C converter or USB to Serial PS2 and converter - converter to another.
* Users can create / add sort into ATmega8 bootloader, so if you want to do enough to do Firmware upgrade via USB.
 
Download

Firmware

UserInterfaceWithDelphi

DLL and Driver

Posted in: DIY usb to serial , Serial to USB Home Made Using ATmega8