Cypress Semiconductor FX2LP Informations techniques Page 90

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EZ-USB FX2 Technical Reference Manual
Page 3-12 EZ-USB FX2 Technical Reference Manual v2.1
These upload and download requests are always handled by the FX2,
regardless
of the state of
the RENUM bit.
The bRequest value 0xA0 is reserved for this purpose. It should never be used for another vendor
request. Cypress Semiconductor also reserves bRequest values 0xA1 through 0xAF; devices
should not use these bRequest values.
A host loader program will typically write 0x01 to the CPUCS register to put the CPU into RESET,
load all or part of the FX2 RAM with firmware, then reload the CPUCS register with 0 to take the
CPU out of RESET. The CPUCS register (at 0xE600) is the only FX2 register that can be written
using the Firmware Download command.
3.9 How the Firmware ReNumerates
Two control bits in the USBCS (USB Control and Status) register control the ReNumeration™ pro-
cess: DISCON and RENUM.
Figure 3-2. USB Control and Status Register
To simulate a USB disconnect, the firmware sets DISCON to 1. To reconnect, the firmware clears
DISCON to 0.
Before reconnecting, the firmware sets or clears the RENUM bit to indicate whether the firmware
or the Default USB Device will handle device requests over endpoint zero: if RENUM=0, the
Default USB Device will handle device requests; if RENUM=1, the firmware will.
3.10 Multiple ReNumerations™
FX2 firmware can ReNumerate™ anytime. One use for this capability might be to
fine tune
an iso-
chronous endpoint’s bandwidth requests by trying various descriptor values and ReNumerating.
USBCS USB Control and Status E680
b7 b6 b5 b4 b3 b2 b1 b0
HSM 0 0 0 DISCON NOSYNSOF RENUM SIGRSUME
R/WRRRR/WR/WR/WR/W
00000100
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