Here is an example of how to interface a PIC18F452 to a PC via the USB port.
The windows-pc (98, Me, 2000, XP, 2003) runs a program (C# application, Microsoft Visual Studio .NET 2003) to communicate with the USB interface, which transfers data to and from the PIC18F452.
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PIC example (18f452) < > USB interface (FT245BM) < > PC program (C# application)
PIC example (18F452:)
The PIC captures the ambient temperature with a SPI sensor TC77. Its value is then transferred to the USB-interface.
USB interface (FT245BM:)
The USB interface will have to be recognized as a device by Windows. Basically, there are two ways of doing this. Either with a VCP (Virtual COM Port) or with a D2XX (Direct) driver. We will use the D2XX driver here for its high speed. It is more complicated to start up than VCP, but why not going the extra mile?
The FT245BM chip comes with a fixed VID (0403) and PID (6001). We can override this with our own VID (ECDE), PID (0001), our own Product Description (TechDesign USB Device 017) and serial number (FEDC0001). These settings are stored in an external SPI EEPROM 93C46. To program these settings, FTDI made a utility called MProg EEPROM programming utility.
When plugging in for the first time and with a blank (or without) EEPROM, you will notice that the interface is seen as “USB device” and after its driver is installed, it will be recognized as a “FTDI FT8U2XX Device”. Now we can program the EEPROM with our custom settings. To do this, run MProg, open the file 017_USB_id.ept and program (choose “Device”, then “Program”). After this, unplug the interface briefly and plug it in again. It will now be recognized as a “TechDesign USB Device 017”. Acknowledge a couple of times to install it and you are done.
Note that this project will also work without an EEPROM, but in that case you will have to make do with the fixed VID & PID.
PC program (C# application:)
A dll file is performing the communication between the C# application and our USB-interface. It must be placed in the same directory as the exe-file below. Acknowledgements to KOPF for providing this dll and the example “USBTransfer.exe” on which this application is based.
The C# application can be run on any Windows 98, Me, 2000, XP, 2003 platform. It will show the temperature reading captured with the PIC (see above). Here is a quick link to its main form. Download the msi (Microsoft installer file) below to install the application.
You need to have Microsoft .NET Framework 1.1 (or higher) installed to be able to run the executable.
For more detail: PIC18F452 to PC USB 2.0 interface with FT245BM