Cypress Semiconductor FX2LP Información técnica Pagina 36

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EZ-USB FX2 Technical Reference Manual
Page 1-10 EZ-USB FX2 Technical Reference Manual v2.1
RAM which can be loaded over the USB. This makes modifications, specification revisions, and
updates a snap.
The FX2’s “smart” SIE performs much more than the basic functions shown in Figur e1-6; it can
perform a full enumeration by itself, which allows the FX2 to connect as a USB device and down-
load code into its RAM while its CPU is held in reset. This added SIE functionality is also made
available to the FX2 programmer, to make development easier and save code and processing
time.
1.11 ReNumeration
Because the FX2’s configuration is soft, one chip can take on the identities of multiple distinct USB
devices.
When first plugged into USB, the FX2 enumerates automatically and downloads firmware and
USB descriptor tables over the USB cable. Next, the FX2 enumerates again, this time as a device
defined by the downloaded information. This patented two-step process, called ReNumeration™,
happens instantly when the device is plugged in, with no hint that the initial download step has
occurred.
Alternately, FX2 can also load its firmware from an external EEPROM.
Chapter 3, "Enumeration and ReNumeration™" describes these processes in detail.
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