Table 1. Special Function Registers
3.5 USB Boot Methods
During the power up sequence, internal logic checks the I
for the connection of an EEPROM whose first byte is either 0xC0
or 0xC2. If found, it uses the VID/PID/DID values in the EEPROM
in place of the internally stored values (0xC0), or it boot-loads the
EEPROM contents into internal RAM (0xC2). If no EEPROM is
detected, FX2LP enumerates using internally stored descriptors.
The default ID values for FX2LP are VID/PID/DID (0x04B4,
0x8613, 0xAxxx where xxx = Chip revision).
Table 2. Default ID Values for FX2LP
0x04B4 Cypress Semiconductor
0x8613 EZ-USB FX2LP
0xAnnn Depends on chip revision
(nnn = chip revision where first
silicon = 001)
Two control bits in the USBCS (USB Control and Status) register,
control the ReNumeration process: DISCON and RENUM. 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
handles device requests over endpoint zero: if RENUM = 0, the
Default USB Device handles device requests; if RENUM = 1, the
firmware services the requests.
3.7 Bus-Powered Applications
The FX2LP fully supports bus powered designs by enumerating
with less than 100 mA as required by the USB 2.0 specification.
3.8 Interrupt System
3.8.1 INT2 Interrupt Request and Enable Registers
FX2LP implements an autovector feature for INT2 and INT4.
There are 27 INT2 (USB) vectors, and 14 INT4 (FIFO/GPIF)
vectors. See EZ-USB Technical Reference Manual (TRM) for
3.8.2 USB Interrupt Autovectors
The main USB interrupt is shared by 27 interrupt sources. To
save the code and processing time that is required to identify the
individual USB interrupt source, the FX2LP provides a second
level of interrupt vectoring, called Autovectoring. When a USB
interrupt is asserted, the FX2LP pushes the program counter to
its stack, and then jumps to the address 0x0043 where it expects
to find a “jump” instruction to the USB Interrupt service routine.
Because the FX2LP’s configuration is soft, one chip can take on
the identities of multiple distinct USB devices.
When first plugged into USB, the FX2LP enumerates automati-
cally and downloads firmware and USB descriptor tables over
the USB cable. Next, the FX2LP 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, without a hint that the initial download
step has occurred.
2. The I
C bus SCL and SDA pins must be pulled up, even if an EEPROM is not connected. Otherwise this detection method does not work properly.
Document #: 38-08032 Rev. *M
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