4 Function Description
FT240X USB 8-BIT FIFO IC Datasheet
Document No.: FT_000626 Clearance No.: FTDI# 259
The FT240X is a USB to parallel FIFO interface device which simplifies USB implementations and reduces
external component count by fully integrating into the device an MTP memory and an integrated clock
circuit which requires no external crystal. It has been designed to operate efficiently with USB host
controllers by using as little bandwidth as possible when compared to the total USB bandwidth available.
4.1 Key Features
Functional Integration. Fully integrated MTP memory, clock generation, AVCC filtering, power-on-reset
(POR) and LDO regulator.
Configurable CBUS I/O Pin Options. The fully integrated MTP memory allows configuration of the
Control Bus (CBUS) functionality and drive strength selection. There are 2 configurable CBUS I/O options.
The configurable options are defined in section 3.5.
The CBUS lines can be configured with any one of these output options by setting bits in the internal MTP
memory. The device is shipped with the most commonly used pin definitions pre-programmed - see
Section 8 for details.
Asynchronous Bit Bang Mode. In asynchronous bit-bang mode, the eight FIFO lines can be switched
from the regular interface mode to an 8-bit general purpose I/O port. Data packets can be sent to the
device and they will be sequentially sent to the interface at a rate controlled by an internal timer
(equivalent to the baud rate pre-scaler. This option will be described more fully in a separate application
note available from FTDI website (www.ftdichip.com).
Synchronous Bit Bang Mode. The FT240X supports synchronous bit bang mode. This mode differs from
asynchronous bit bang mode in that the interface pins are only read when the device is written to. This
makes it easier for the controlling program to measure the response to an output stimulus as the data
returned is synchronous to the output data. An application note, AN232R-01, available from FTDI website
(www.ftdichip.com) describes this feature.
High Output Drive Option. The parallel FIFO interface and the four FIFO handshake pins can be made
to drive out at three times the standard signal drive level thus allowing multiple devices to be driven, or
devices that require a greater signal drive strength to be interfaced to the FT240X. This option is
configured in the internal MTP memory.
Programmable FIFO RX Buffer Timeout. The FIFO RX buffer timeout is used to flush remaining data
from the receive buffer. This timeout defaults to 16ms, but is programmable over USB in 1ms increments
from 2ms to 255ms, thus allowing the device to be optimised for protocols that require fast response
times from short data packets.
Wake Up Function. If USB is in suspend mode, and remote wake up has been enabled in the internal
MTP memory (it is enabled by default). Strobing the SIWU# pin low for a minimum of 20ms will cause
the FT240X to request a resume from suspend on the USB bus. Normally this can be used to wake up the
host PC from suspend.
Source Power and Power Consumption. The FT240X is capable of operating at a voltage supply
between +3.3V and +5.25V with a nominal operational mode current of 8mA and a nominal USB suspend
mode current of 125µA. This allows greater margin for peripheral designs to meet the USB suspend mode
current limit of 2.5mA. An integrated level converter within allows the FT240X to interface to logic
running at +1.8V to +3.3V (5V tolerant).
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