USB Interface

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4.1Self Powered Device

Figure 4-1shows the USB interface connection for a self-powered device. The 0 ohm resistors are optional, and if not used, then connect USB UDC+ directly to the device UDC+ and connect USB UDC- directly to device UDC-. The device UDC+ and UDC- pins match the impedance of a USB cable, 90 ohms, without the use of external series resistors. You may install 0 ohm resistors on your board to compensate for minor differences between the USB cable and your board trace impedance.

The 5 to 3.3 voltage divider is required since the device GPIO pins cannot exceed 3.3 V. This voltage divider can be implemented in a number of ways. The most robust and expensive solution is to use a MAX6348 Power-On-Reset device. This solution produces a very clean signal edge and minimizes signal bounce. The more inexpensive solution is to use a 3.3 V line buffer with 5 V tolerant inputs. This solution does not reduce signal bounce, so software must compensate by reading the GPIO signal after it stabilizes. A third solution is to implement a signal bounce minimization circuit that is 5 V tolerant, but produces a 3.3 V signal to the GPIO pin.

Note: If GPIOn and GPIOx are the same pin, never put the device to sleep while the USB cable is connected to the device. During sleep, the USB controller is in reset and will not respond to the host; after sleep, the device will not respond to its host-assigned address.

Figure 4-1. Self Powered Device

USB 5V

USB UDC+

USB UDC-

USB GND

5V to 3.3V

470K

GPIOn

GPIOx

1.5K

UDC+

0ohm

(optional)

UDC-

0ohm

(optional)

Board GND

4.1.1Operation if GPIOn and GPIOx are Different Pins

Any GPIO pins can be defined as GPIOn and GPIOx. GPIOn should be a GPIO which can bring the device out of sleep. Out of reset, configure GPIOx as an input that causes the UDC+ line to float. GPIOn is configured as an input that causes an interrupt whenever a rising or falling edge is

PXA250 and PXA210 Applications Processors Design Guide

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Intel PXA250 and PXA210 manual USB Interface, Self Powered Device, Operation if GPIOn and GPIOx are Different Pins

PXA250 and PXA210 specifications

The Intel PXA250 and PXA210 processors, part of the Intel XScale architecture, were introduced in the early 2000s, targeting mobile and embedded applications. They are known for their low power consumption, high performance, and advanced multimedia capabilities, making them suitable for a wide range of devices, including PDAs, smartphones, and other portable computing devices.

The PXA250, which operates at clock speeds ranging from 400 MHz to 624 MHz, features a superscalar architecture that allows it to issue multiple instructions per clock cycle. This enhances the overall performance for demanding applications while maintaining low power usage. It supports a variety of peripheral interfaces, including USB, Ethernet, and various memory types, which contributes to its versatility in different product designs.

One of the key technologies in the PXA250 is the integrated Intel Smart Repeat Technology, which optimizes data processing, thereby reducing the amount of power consumed during operation. This feature is particularly important for battery-powered devices, as it extends the overall battery life, allowing for longer usage times in mobile environments. Additionally, the PXA250 includes a dedicated graphics acceleration unit, which enables enhanced graphics and multimedia performance suited to modern applications at the time.

In contrast, the PXA210 is a more entry-level processor, aimed at cost-sensitive applications. Operating at lower clock speeds, typically around 200 MHz to 400 MHz, it forgoes some of the advanced performance features of the PXA250 while still offering a good balance of performance and power efficiency. The PXA210 is less complex, making it suitable for simpler devices that do not require the extensive capabilities of the PXA250.

Both processors utilize the Intel XScale architecture, which is based on the ARM instruction set. They are built on a 0.13-micron process technology, enabling higher density and lower power consumption compared to their predecessors. With integrated memory controllers and bus interfaces, they facilitate efficient data handling and connectivity options.

In summary, both the Intel PXA250 and PXA210 processors played a crucial role in the evolution of mobile computing by providing powerful processing capabilities with energy efficiency. Their features and technologies enabled device manufacturers to create innovative products that catered to the growing demand for portable devices during that era.