FT4232HL-TRAY International Semiconductor Technologies, FT4232HL-TRAY Datasheet - Page 19

• Manufacturer Part Number: FT4232HL-TRAY
• Description: Specifications: Number of Channels: 4, QUART ; Lead Free Status: Lead Free ; RoHS Status: RoHS Compliant
• Manufacturer: International Semiconductor Technologies

Document No.: FT_000060
FT4232H QUAD HIGH SPEED USB TO MULTIPURPOSE UART/MPSSE IC
Datasheet Version 2.2
Clearance No.: FTDI#78
4.3.3 RS485 Configuration
Figure 4.3 illustrates how the FT4232H can be configured as a dual RS485 interface. The FT4232H can
have all 4 channels connected as RS485, but only channel A and channel C are shown for clarity.
Figure 4.3 Dual RS485 Configuration
In this case both channel A and channel C are configured as RS485 operating at TTL levels and a level
converter device (half duplex RS485 transceiver) is used to convert the TTL level signals from the
FT232H to RS485 levels. 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
FT4232H 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 FT4232H 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 FT4232H it is possible to do this entirely in hardware – simply
modify the schematic so that RXD of the FT4232H is the logical OR of the level converter device receiver
output with TXDEN using an HC32 or similar logic gate
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