The USB device consisted of a microphone, the microprocessor and other hardware and the device sent audio data to the host computer. Hopefully this information will be helpful to your project. Table of Contents Results - the project worked! This involved building the device hardware microprocessor, microphone, and supporting electronics and software microprocessor code and host computer code.
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The USB device consisted of a microphone, the microprocessor and other hardware and the device sent audio data to the host computer.
Hopefully this information will be helpful to your project. Result We achieved our goal and built a working device. This involved building the device hardware microprocessor, microphone, and supporting electronics and software microprocessor code and host computer code. To top. There are lots of other features of USB. The specifications for USB are available at www. Be warned that while this information is very thorough, it is not very practical for developing a device or software.
Technical documents are available at www. Here is a quick overview of what is involved in USB. The signal wires usually operate in differential mode one is high while the other is low. There are two types of USB devices: high speed and low speed. There are differences in the type, length and connectors that can be used with the two types.
Generally the requirements are stricter for high speed devices. A high speed device can transfer data at a maximum of 12 Mbs while low speed is limited to 1. The PIC 16C can only operate at low speed standard.
The connector at the computer A End is a flattened rectangle while at the device B end the connector is square with two cut-off corners necessary to be compliant with the high-speed standard but optional for low speed devices. Each USB device is able to draw mA from the cable which allows a device to be bus powered. A device can negoiate up to mA once connected to the USB cable but this power may not be available.
If the power is unavailable the device must stay in a low power setting. Obviously devices can be powered externally as well. The Software: When a device is connected, the computer or a hub detects the device by a pullup resister see circuit. When detected a series of enumeration steps are started. The enumeration process assigns an identifier number to the device there can be a maximum of devices on a network and also tells the host computer what sort of capabilities a device has input, ouput, etc.
If the device identifies itself as a HID Human Interface Device then the device describes how the data should be interpreted. See the section on HID. During the enumeration process, the device describes the information that it can receive and send.
This allows a host computer to handle the data being received from the USB device without requiring a specially designed device driver. Because the host computer knows what the data means a device driver is not necessary for HID devices, the operating system can supply a generic HID driver. For instance, if you plug in a USB Mouse, it will immediately work because the OS knows how to interpret information received from a mouse. Information on the HID class can be found at www.
Some other useful tools are available from Intel University Press[ 1 ]. Unfortunately the program is more complicated than it needs to be and is not a good example of using the USB functions. This chip belongs to a two chip family along with the 16C called the 16c7xx.
The 16C is a 28 pin microprocessor operating at 24 Mhz. It has 8K of program memory, bytes of RAM and 5 x 8bit analog inputs the 16C has 40 pins and 8 analog inputs.
The specifications are available from Microchip. The reference manual for the mid-range microprocessors is also useful. Another necessary component is the USB firmware. The support files that I used seem to no longer exist on the Microchip web site being replaced by a more sophisticated USB example. The firmware includes the following pieces:.
USB and PIC Microprocessors 16C745 and 18F2455
TOOLS for the PIC16C745
USB PIC projects
usb interfacing through vb6.0