Cypress Semiconductor FX2LP Informações Técnicas Página 83

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Chapter 3. Enumeration and ReNumeration™ Page 3-5
3.4.2 Serial EEPROM Present, First Byte is 0xC0
If, at power-on reset, the FX2 detects an EEPROM connected to its I²C-compatible bus with the
value 0xC0 at address 0, the FX2 automatically copies the Vendor ID (VID), Product ID (PID), and
Device ID (DID) from the EEPROM (Table 3-4) into internal storage. The FX2 then supplies these
EEPROM bytes to the host as part of its response to the host’s Get_Descriptor-Device request
(these six bytes replace only the VID / PID / DID bytes in the Default USB Device descriptor). This
causes a host driver matched to the VID / PID / DID values in the EEPROM to be loaded by the
host OS.
After initial enumeration, that host driver downloads FX2 firmware and USB descriptor data into the
FX2’s RAM and starts the CPU. The FX2 then ReNumerates™ as a custom device. At that point,
the host may load a new driver, bound to the just-loaded VID / PID / DID.
The eighth EEPROM byte contains configuration bits that control the following:
I²C-compatible bus speed.
Default is 100 KHz
.
Disconnect polarity.
Default is for FX2 to come out of reset connected to USB
.
FX2 firmware can change the I²C-compatible bus speed using control-register bits, so an
EEPROM is not required in order to override the default setting. However, the firmware cannot
modify the disconnect polarity; if it’s desired for the FX2 to come out of reset disconnected from
USB, a “C0” or “C2” EEPROM must be connected.
Section 3.5 "EEPROM Configuration Byte" contains a full description of the configurations bits.
Table 3-4. “C0 Load” Format
EEPROM Address Contents
0
0xC0
1 Vendor ID (VID) L
2 Vendor ID (VID) H
3 Product ID (PID) L
4 Product ID (PID) H
5 Device ID (DID) L
6 Device ID (DID) H
7 Configuration byte
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