Cypress Semiconductor FX2LP Specifikace stáhnout pdf (Strana 3)

Migrating From EZ-USB FX2™ to EZ-USB FX2LP™

www.cypress.com Document No. 001-42079 Rev. *D 3



FX2LP has internal memory from 0x0000 to 0x3FFFF

as opposed to FX2 that has internal memory from

0x0000 to 0x1FFFF. Check the code location to make

sure whether the existing FX2 application uses

memory mapped ROM (any nonvolatile memory) or

memory mapped I/O within the address space of

0x2000 to 0x3FFF. If so, they must be mapped to new

locations and the firmware should be re linked as the

FX2LP accesses the internal memory that is not the

intended access method of the end application. In the

limited number of designs that require this change,

just a logic change to an FPGA or programmable logic

array for hardware memory decoding and changing

the target location of the external code within the

compiler/linker is needed. If the existing FX2 design

has RAM at this location (0x2000 to 0x3FFF), no

changes are required while replacing the part with

FX2LP.



If the FX2 application use high-bandwidth Isochronous

IN transfer, and if it has a workaround (on the host

end or the device end) for handling the possible

occurrence of a scenario of data PID mismatch:

additional hardware, external logic, or software on the

host end to handle the scenario, then you may

consider removing the additional logic/code as the

FX2LP has resolved this data PID mismatch issue.

You may also choose to not remove the designed

workaround for ease of drop-in replacement with

FX2LP

Note While changing components such as the USB

controller (FX2 to FX2LP), the USB-IF requires a rerun of

certification test. The following section provides details on

the specifications on every change that is mentioned

earlier.

Details of the Hardware Changes

An overview of the essential hardware changes/additions

in the FX2LP are listed below:



Changes to crystal specification



Minimum reset time



ramp-up time



Changes to AVCC/AGND Pin Functionality

Changes to Crystal Specification

With the use of FX2LP one change is required. When a

crystal is used in the design, for proper operation the load

capacitance of the crystal must change. This affects both

the load capacitors and the crystal being used. The

CY7C68013 requires a crystal with load capacitors that

are between 20 pF and 33 pF. The CY7C68013A requires

a crystal with load capacitors of 12 pF. If redesigning an

FX2 application with FX2LP, the crystal must change to a

load capacitance of 12 pF, and the matching load

capacitors must change to 12 pF. This is a requirement of

all designs using FX2LP. Following is the spec on the

crystal:



24 MHz +100 ppm



Parallel resonant



Fundamental mode



500 W drive level



12-pF (5% tolerance) load cap

One of the parts we recommend is one from ECS Inc.

International: ECS-240-20-4.

The above specification must be taken into consideration

while selecting both the load capacitors and the crystal.

Using a different crystal load capacitance with a crystal

specified for 12 pF is expected to have some effect on the

frequency shift. It is recommended that the designer

always make sure that the power dissipated by the crystal

is within the crystal manufacturer’s specifications. Over-

driving the crystal may damage the crystal. See the

specific crystal manufacturer’s recommendations.

An article on crystal design and selection from Ecliptek's

site states the following:

“The rate of aging is typically greatest during the first 30 to

60 days after which time the aging rate decreases. The

following factors effect crystal aging: adsorption and

desorption of contamination on the surfaces of the quartz,

stress relief of the mounting and bonding structures,

material outgassing, and seal integrity.”

One of the effects of over-driving the crystal out of its

specified conditions may be aging of the crystal that is

expected to result in frequency shift. From speaking to

various crystal manufacturers, we have been informed that

the majority of the shift due to aging usually occurs in the

first 45–60 days or so.

In general, it is recommended that a designer always

make sure that the power dissipated by the crystal is

within the crystal manufacturer’s specifications. Over-

driving the crystal 'may' have adverse effects on the

crystal performance and accuracy. It is also recommended

that the user refer to the crystal manufacturer’s

recommendations on the various effects of driving a

crystal beyond its specified values.

Using a 16-pF or 20-pF crystal or any other standard load

capacitance, may work as indicated by the discussions we

have had with various crystal manufacturers. But using

this is at the customer’s discretion as the FX2LP part was

only tested and designed for a 12-pF, 24-MHz crystal.

Please consult with the specific crystal manufacturer for

information on the various effects of driving a crystal

beyond its specified values. When a crystal is used in the

design using FX2LP, Cypress recommends that for proper

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