FT245BM USB FIFO ( USB - Parallel ) I.C.
•
Serial Interface Engine (SIE)
The Serial Interface Engine (SIE) block performs
the Parallel to Serial and Serial to Parallel
conversion of the USB data. In accordance to the
USB 2.0 specification, it performs bit stuffing / un-
stuffing and CRC5 / CRC16 generation / checking
on the USB data stream.
•
•
USB Protocol Engine
The USB Protocol Engine manages the data
stream from the device USB control endpoint. It
handles the low level USB protocol (Chapter 9)
requests generated by the USB host controller
and the commands for controlling the functional
parameters of the FIFO.
•
FIFO Receive Buffer (128 bytes)
Data sent from the USB Host to the FIFO via
the USB data out endpoint is stored in the FIFO
Receive Buffer and is removed from the buffer by
reading the FIFO contents using RD#.
•
FIFO Transmit Buffer (384 bytes)
Data written into the FIFO using WR# is stored in
the FIFO Transmit Buffer. The Host removes Data
from the FIFO Transmit Data by sending a USB
request for data from the device data in endpoint.
FIFO Controller
The FIFO Controller handles the transfer of data
between the external FIFO interface pins and the
FIFO Transmit and Receive buffers.
RESET Generator
The Reset Generator Cell provides a reliable
power-on reset to the device internal circuitry
on power up. An additional RESET# input and
RSTOUT# output are provided to allow other
devices to reset the FT245BM, or the FT245BM
to reset other devices respectively. During reset,
RSTOUT# is driven low, otherwise it drives out
at the 3.3V provided by the onboard regulator.
RSTOUT# can be used to control the 1.5K
pull-up on USBDP directly where delayed USB
enumeration is required. RSTOUT# will be low for
approximately 5ms after VCC has risen above 3.5V
AND the device oscillator is running AND RESET#
is high. RESET# should be tied to VCC unless it
is a requirement to reset the device from external
logic or an external reset generator I.C.
EEPROM Interface
Though the FT245BM will work without the optional
EEPROM, an external 93C46 (93C56 or 93C66)
EEPROM can be used to customise the USB VID,
PID, Serial Number, Product Description Strings
and Power Descriptor value of the FT245BM for
OEM applications. Other parameters controlled
by the EEPROM include Remote Wake Up,
Isochronous Transfer Mode, Soft Pull Down on
Power-Off and USB 2.0 descriptor modes.
The EEPROM should be a 16 bit wide
configuration such as a MicroChip 93LC46B or
equivalent capable of a 1Mb/s clock rate at VCC =
4.35V to 5.25V. The EEPROM is programmable-
on board over USB using a utility available from
FTDI’s web site (
). This
allows a blank part to be soldered onto the PCB
and programmed as part of the manufacturing and
test process.
If no EEPROM is connected (or the EEPROM
is blank), the FT245BM will use its built-in
default VID, PID Product Description and Power
Descriptor Value. In this case, the device will not
have a serial number as part of the USB descriptor.
•
•
DS245B Version 1.7
© Future Technology Devices Intl. Ltd. 2005
Page 6 of 24
FTDI [ FUTURE TECHNOLOGY DEVICES INTERNATIONAL LTD. ]
