Copyright © 2010 Future Technology Devices International Limited 15
Document No.: FT_000173
FT2232D DUAL USB TO SERIAL UART/FIFO IC Datasheet
Version 2.05
Clearance No.: FTDI# 127
4.1 Functional Block Descriptions
The following paragraphs detail each function within the FT2232D. Please refer to the block diagram
shown in Figure 2.1.
3.3V LDO Regulator: The 3.3V LDO Regulator generates the 3.3 volt reference voltage for driving the USB
transceiver cell output buffers. It requires an external decoupling capacitor to be attached to the 3V3OUT
regulator output pin. It also provides 3.3V power to the RSTOUT# pin. The main function of this block is to
power the USB Transceiver and the Reset Generator Cells rather than to power external logic. However,
external circuitry requiring 3.3V nominal at a current of not greater than 5mA could also draw its power from
the 3V3OUT pin if required
USB Transceiver: The USB Transceiver Cell provides the USB 1.1 or USB 2.0 full-speed physical interface
to the USB cable. The output drivers provide 3.3 volt level slew rate control signalling, whilst a differential
receiver and two single ended receivers provide USB data in, SEO and USB Reset condition detection.
USB DPLL: The USB DPLL cell locks on to the incoming NRZI USB data and provides separate recovered
clock and data signals to the SIE block.
6MHz Oscillator: The 6MHz Oscillator cell generates a 6MHz reference clock input to the x8 Clock
multiplier from an external 6MHz crystal or ceramic resonator.
x8 Clock Multiplier: The x8 Clock Multiplier takes the 6MHz input from the Oscillator cell and generates a
48MHz reference clock for the USB DPPL and the Baud Rate Generator blocks.
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 UART / FIFO controller blocks.
Dual Port TX Buffers (128 bytes): Data from the USB data out endpoint is stored in the Dual Port TX
buffer and removed from the buffer to the transmit register under control of the UART FIFO controller.
Dual Port RX Buffers (384 bytes): Data from the UART / FIFO controller receive register is stored in the
Dual Port RX buffer prior to being removed by the SIE on a USB request for data from the device data in
endpoint.
Multi-Purpose UART / FIFO Controllers: The Multi-purpose UART / FIFO controllers handle the transfer
of data between the Dual Port RX and TX buffers and the UART / FIFO transmit and receive registers. When
configured as a UART it performs asynchronous 7 / 8 bit Parallel to Serial and Serial to Parallel conversion of
the data on the RS232 (RS422 and RS485) interface. Control signals supported by UART mode include RTS,
CTS, DSR, DTR, DCD and RI. There are also transmitter enable control signal pins (TXDEN) provided to
assist with interfacing to RS485 transceivers. RTS/CTS, DSR/DTR and Xon/Xoff handshaking options are
also supported. Handshaking, where required, is handled in hardware to ensure fast response times. The
UART‟s also supports the RS232 BREAK setting and detection conditions.
Baud Rate Generator: The Baud Rate Generator provides a x16 clock input to the UART‟s from the 48MHz
reference clock and consists of a 14 bit prescaler and 3 register bits which provide fine tuning of the baud
rate (used to divide by a number plus a fraction). This determines the Baud Rate of the UART which is
programmable from 183 baud to 3 million baud.
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 FT2232D, or the FT2232D 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. It can also be used to reset
other devices. RSTOUT# will stay high- impedance 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: When used without an external EEPROM the FT2232D be configured as a USB to dual
serial port device. Adding an external 93C46 (93C56 or 93C66) EEPROM allows each of the chip‟s channels
to be independently configured as a serial UART (232 mode), or a parallel FIFO (245 mode). The external
EEPROM is used to enable the Fast Opto-Isolated Serial interface mode.
The external EEPROM can also be used to customise the USB VID, PID, Serial Number, Product Description
Strings and Power Descriptor value of the FT2232D for OEM applications. Other parameters controlled by
the EEPROM include Remote Wake Up, 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 program available from FTDI‟s web
site (www.ftdichip. com). 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 FT2232D
will default to dual serial ports. The device uses 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.