Beefing up the Cortex-M3-based MCU to Handle 480 Mbps High-speed USB

The universal serial bus (USB) has completely replaced UART, PS2, and IEEE-1284 parallel interfaces on PCs, and now is gaining wide acceptance in embedded applications. Most of the I/O devices (keyboards, scanners, mice) used with embedded systems are USB-based for good reason.

Since the USB is a well-defined standard that is guaranteed by the USB consortium, any USB-certified device from any vendor will work in a plug-and-play fashion with any USB-certified device from any other vendor.

Multiple devices can operate on the same bus without affecting each other at all. It is not at all surprising that the majority of 32-bit flash MCU and MPU vendors offer some form of USB interface as a standard peripheral: USB host, USB device, USB OTG " usually limited to the "full-speed" specification of 12 Mbps (Figure 1, below).


 
Figure 1. USB Block Diagram

Now, the USB standard is set to solve another issue for embedded systems: the exponential growth in data rates. Five years ago, a data rate of 10 Mbps was considered high. A 12 Mbps full-speed USB, 10 Mbps SPI or 400 kps I2C interface could cover the data requirements of nearly any embedded application.

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