FT245BM USB FIFO ( USB - Parallel ) I.C.
approach allows a customer to create a “generic”
USB peripheral who’s hardware function can be
defined under control of the application software.
The FPGA based hardware can be easily upgraded
or totally changed simply by changing the FPGA
configuration data file. Application notes, software
and development modules for this application area
will be available from FTDI and other 3
rd
party
developers.
•
Less External Support Components
As well as eliminating the RCCLK RC network, and
for most applications the need for an external reset
circuit, we have also eliminated the requirement
for a 100K pull-up on EECS to select 6MHz
operation. When the FT245BM is being used
without the configuration EEPROM, EECS, EESK
and EEDATA can now be left n/c. For circuits
requiring a long reset time (where the device is
reset externally using a reset generator I.C., or
reset is controlled by the IO port of a MCU, FPGA
or ASIC device) an external transistor circuit is
no longer required as the 1.5K pull-up resistor on
USBDP can be wired to the RSTOUT# pin instead
of to 3.3V. Note : RSTOUT# drives out at 3.3V
level, not at 5V VCC level. This is the preferred
configuration for new designs.
•
Extended EEPROM Support
The previous generation of devices only supported
EEPROM of type 93C46 (64 x 16 bit). The new
devices will also work with EEPROM type 93C56
(128 x 16 bit) and 93C66 (256 x 16 bit). The extra
space is not used by the device, however it is
available for use by other external MCU / logic
whilst the FT245BM is being held in reset.
•
USB 2.0 ( full speed option )
A new EEPROM based option allows the FT245BM
to return a USB 2.0 device descriptor as opposed
to USB 1.1. Note : The device would be a USB 2.0
•
EEREQ# / EEGNT#
These (FT8U245AM) pins are no longer supported
on the FT245BM device. They have been replaced
with the new SI / WU and PWREN# signals
respectively.
•
Multiple Device Support without EEPROM
When no EEPROM (or a blank or invalid
EEPROM) is attached to the device, the FT245BM
no longer gives a serial number as part of its
USB descriptor. This allows multiple devices to
be simultaneously connected to the same PC.
However, we still highly recommend that EEPROM
is used, as without serial numbers a device can
only be identified by which hub port in the USB tree
it is connected to which can change if the end user
re-plugs the device into a different USB port.
Full Speed device (12Mb/s) as opposed to a USB
2.0 High Speed device (480Mb/s).
DS245B Version 1.7
© Future Technology Devices Intl. Ltd. 2005
Page 4 of 24
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