FT2232D datasheet(32/56 Pages) FTDI

32 / 56 page

DS2232D Version 0.91

FT2232D Dual USB UART / FIFO I.C.

Figure 16 - USB <=> RS485 Converter Configuration

Figure 16 illustrates how to connect the UART interfaces of the FT2232D to two TTL – RS485 Level Converter I.C.’s

to make a USB to dual port RS485 converter. This example uses two Sipex SP491 devices but there are similar parts

available from Maxim and Analog Devices amongst others. The SP491 is a RS485 device in a compact 8 pin SOP

package. It has separate enables on both the transmitter and receiver. With RS485, the transmitter is only enabled

when a character is being transmitted from the UART. The TXDEN pins on the FT2232D are provided for exactly that

purpose, and so the transmitter enables are wired to the TXDEN’s. The receiver enable is active low, so it is wired to

the PWREN# pin to disable the receiver when in USB suspend mode.

RS485 is a multi-drop network – i.e. many devices can communicate with each other over a single two wire cable

connection. The RS485 cable requires to be terminated at each end of the cable. Links are provided to allow the cable

to be terminated if the device is physically positioned at either end of the cable.

In this example the data transmitted by the FT2232D is also received by the device that is transmitting. This is a

common feature of RS485 and requires the application software to remove the transmitted data from the received

data stream. With the FT2232D it is possible to do this entirely in hardware – simply modify the schematic so that RXD

of the FT2232D is the logical OR of the SP481 receiver output with TXDEN using an HC32 or similar logic gate.

DB9-M

RS485 Channel A

DM_A

GND

120R

DPA

VCC

SP481

LINK

FT2232C

SLEEP# (ACBUS1)

TXD (ADBUS0)

RXD (ADBUS1)

RTS# (ADBUS2)

CTS# (ADBUS3)

DTR# (ADBUS4)

DSR# (ADBUS5)

DCD# (ADBUS6)

RI# (ADBUS7)

TXDEN (ACBUS0)

PWREN#

SLEEP# (BCBUS1)

TXD (BDBUS0)

RXD (BDBUS1)

RTS# (BDBUS2)

CTS# (BDBUS3)

DTR# (BDBUS4)

DSR# (BDBUS5)

DCD# (BDBUS6)

RI# (BDBUS7)

TXDEN (BCBUS0)

DB9-M

RS485 Channel B

DM_B

GND

120R

DP_B

VCC

SP481

LINK

FT2232D

FT2232D Datasheet(PDF) 32 Page - Future Technology Devices International Ltd.

FT2232D Datasheet(HTML) 32 Page - Future Technology Devices International Ltd.

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