Usb Microcontroller Communications Architecture for Human Interface gadget (Hid)

The Usb communications architecture is designed to enable computing devices such as desktop Pcs and laptops to interconnect with many other peripheral devices. A Usb uses a two wire serial communications link running at one of three distinct speeds: 1.5 megabits per second (low speed), 12 Mbps (full speed) and 480 Mbps (high speed). Usb devices are categorized into various expedient classes such as display, communication, audio, mass storage and human interface.

The Human Interface expedient (Hid) Class defines base behaviors and functions for touch screen interfaces. The Hid class includes peripherals such as keyboards, mice, trackballs, joysticks, touch pads and touch screens that enable end users to operate and interact with the computing system. Hid also includes provisions for yield directed to the end user. The Hid specification requires one operate endpoint and one interrupt endpoint with the host.

The operate pipe typically handles enumeration and expedient configuration while the interrupt pipe is used for data transfer. Descriptors define a Usb expedient to the host with regard to the type of device, the expedient manufacturer, Usb1.x or 2.0 or 3.0 support, expedient configuration, endpoints quantities and types, etc. Touch screen expedient descriptors tell the host which endpoints and transfer types are supported. In expanding to handling appropriate Usb requests, Hid devices must talk to all appropriate Hid requests. Data must be transferred within defined structures called reports, which can be transferred across either the operate pipe or interrupt pipe.

Hid devices can transfer data stored in reports with the host through the operate pipes. This transfer is typically reserved for configuration data or expedient identification. The Usb specification defines the transfer sequence for the operate pipe, which has a higher level of error checking than other transfer methods. The host application programming interface (Api) calls used to send data through the operate pipe differ from those used for the interrupt pipe. During enumeration, the expedient requests how often it wants the host to ask for the data or send the data. After enumeration is complete, the host schedules data transfers on a periodic basis. If the enumerated expedient is a touch screen, the touch screen Usb bridge or the touch controller (e.g., a controller that supports Usb natively) assembles the coordinates of the finger(s), as well as other related data such as finger width, signal strengths, finger speed and gestures, and shop that data in a buffer. The data is transmitted to the host at the interval specified previously or upon determined events such as a finger's touch.

Usb Microcontroller Communications Architecture for Human Interface gadget (Hid)

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Jtag - approved Test way Port and Boundary - Scan Architecture

When you have an integrated circuit (Ic) or many such devices on a board, where each Ic has 100 or more pins, it is mandatory to have some tool to test connections and verify operation. Having this in mind, an expert group ready a specification for testing that was standardized in 1990 as the Ieee Std. 1149.1. It is also known as the Jtag (Joint Test activity Group) standard.

Jtag is a formula for testing connections on printed circuit boards (Pcbs) that are implemented at the integrated circuit (Ic) level. It is very difficult to test involved circuits with traditional in-circuit testers. Because of corporeal space constraints and inability to access very small components and Bga devices, the cost for board testing has increased significantly. Jtag is an elegant clarification to overcome problems with corporeal in-circuit testers.

With Jtag you can test interconnects in the middle of integrated circuits on a board without using corporeal test probes. This is a big advantage because you don't need any further customized tool for testing. Of course, the device has to be Jtag enabled. This means an further cell (a boundary-scan cell) for each pin. Boundary-scan cell can set or read data on each pin. Boundary-scan cells are associated together and the data is serially shifted into the boundary-scan cells. The process is controlled from a serial data path called the scan path or scan chain. This is the basic principle of the Jtag interface.

Jtag eliminates the need for a large whole of test vectors, which would be needed to initialize all the devices. Using Jtag means shorter test times, increased diagnostic ability higher test coverage, and lower equipment cost. Although there are many variations of the Jtag header on the board it is potential to use suitable Jtag signals with almost any Jtag interface and boundary-scan software.

An further advantage with Jtag interface is that it can be also used for programming and debugging. Many microcontrollers, Flash memories, Fpgas and similar devices can be programmed via Jtag interface. And the same interface can be used for debugging. Jtag is a big step toward suitable interfaces in electronics industry.

There are many Jtag cables that can be used on more than one device. In fact, Jtag cable is more than a cable. Regularly it has some small electronics to boost signals and to provide suitable computer interface. The price of the simplest Jtag cable can be as low as .

Jtag - approved Test way Port and Boundary - Scan Architecture

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