Migrating From EZ-USB FX2™ to EZ-USB FX2LP™
www.cypress.com Document No. 001-42079 Rev. *D 2
Difference between FX2 and FX2LP
Following table provides a brief overview of the difference
between FX2 and FX2LP.
at least 200 s with
ramp rate of 18 V/ms
2 additional
AVCC/AGND pins
Disabling high-
speed chirp through
EEPROM
Operates in full-
speed, can
renumerate as high-
speed through
firmware modification
Operates only in
Full-speed
Pull-up on D+ present
even when RESET#
asserted
pull-up on D+
disabled when
RESET# asserted
Isochronous Zero-
length packet (ZLP)
support
Does not send ZLP
when no data
available in SIE in
response to
isochronous IN
request
Capable of sending
ZLP when no data
available in SIE in
response to
isochronous IN
request
Moderate power
(260mA maximum)
Lower power (85mA
maximum)
Comes up enabled
during power-up
Comes up disabled
during power-up
FIFO address hold-
time for Slave FIFO
asynchronous write
ECC generation on
GPIF data
Migrating from FX2 to FX2LP
Hardware Changes
Following are a list of required changes when replacing
the FX2 in a existing design with FX2LP:
Make sure to replace the crystal with the appropriate
load capacitors. The FX2LP requires a crystal with
load capacitors of 12 pF.
Make sure that the reset is held for at least 5 ms.
Make sure that the V
CC
ramp-up time is at least 200 s
with a ramp rate of 18 V per millisecond.
Changes on AVCC/AGND pin functionality (see
Changes on AVCC/AGND Pin Functionality on page
4).
Note After installing CY3684 EZ-USB FX2LP
Development Kit, the hardware collateral of the kit
available at location C:\Cypress\USB\Hardware (Location
varies based on installation) can be used as a reference to
develop the board.
Firmware Changes
As next generation of the FX2, the FX2LP has some
enhanced features that the user may want to take
advantage of or may decide to simply disregard. Based on
the application’s needs these enhancements in the FX2LP
may require some changes in the designer’s FX2-based
application. Following is a list of things that the designer
needs to be informed when replacing the FX2 in a existing
design with FX2LP.
Is the existing FX2 application bus-powered and does
it have the double enumeration workaround for
meeting the unconfigured current limit of 100 mA. If
so, set the control bit of the EEPROM to 0 (chip
enabled) as the workaround is not required anymore.
The FX2LP meets the 100-mA current requirement for
unconfigured current. You may opt to either leave in
or remove the double enumeration workaround in the
firmware.
The FX2LP automatically disconnects and
subsequently reconnects on a hard reset (asserting
RESET# pin). If the FX2 firmware has the 8051 do the
disconnect and reconnect manually by setting and
clearing DISCON bit of the USBCS register on a hard
reset, it is not required anymore. Based on your
application’s needs, when porting the same firmware
to FX2LP, you may opt to either leave in or remove
the code that does this disconnect and reconnect
manually. This needs to be evaluated on an
application basis and the effects (if any) on the system
as a whole on disconnecting and reconnecting twice
(if the 8051 code is left in the firmware ported to
FX2LP).
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