FT232BM USB UART ( USB - Serial) I.C.
•
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 FT232BM 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 FT232BM is being held in reset.
•
USB 2.0 (full speed option)
A new EEPROM based option allows the FT232BM
to return a USB 2.0 device descriptor as opposed to
USB 1.1. Note : The device would be a USB 2.0 Full
Speed device (12Mb/s) as opposed to a USB 2.0
High Speed device (480Mb/s).
•
Multiple Device Support without EEPROM
When no EEPROM (or a blank or invalid
EEPROM) is attached to the device, the FT232BM
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 port.
DS232B Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 4 of 25
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