DS_FT2232D Datasheet, PDF (34/61 Pages) List of Unclassifed Manufacturers – Future Technology Devices International Ltd

Document No.: FT_000173
FT2232D DUAL USB TO SERIAL UART/FIFO IC Datasheet
Version 2.05
Clearance No.: FTDI# 127
Figure 8.3 USB <=> Dual Port RS485 Converter Configuration
Figure 8.3 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
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