It is time to use USB. After several unsuccessful experiments I found some working project in the internet. Maybe other project are working too, but only this one was usable and understandable for me. As I need not only binary compatibility, but compatibility in the source code level. I want to recompile all stuff by myself. In this project only USB Windows system drivers are downloaded from sourceforge web pages.
Why designing the PCB I looked to several other project and adapted my circuit diagram to accept several types of connections. With slight modifications, it is possible to use other firmware.
So, the USB- Universal Serial Buss. This “universal” means that this system is multipurpose and more complicated. It is not only serial data transfer, but stack of procedures, drivers and other stuff to connect external devices to master unit using same buss. It is more complicated that old RS232 serial one and it is very hard to implement all features to simple device. Also, as this buss is “universal” globally, there are some limitations- every device must have unique identification. This identification is coordinated by some organization. This organization distributes VIN (vendor identification number) for money. We shall use free, testing numbers. All software is distributed under GPL/LGPL licenses, so fell free to use it. USB firmware is used from http://www.obdev.at/products/avrusb/index.html. VIN/PIN (also called VID/PID) is used from same source.
Also, LCD module is used to test this project.
There is small testing software for Windows to test the device. It allows to print text on the LCD and some other small command. The source code will be in the next post as I have problems with compiling it with my compiler.