FT4232H QUAD HIGH SPEED USB TO MULTIPURPOSE UART/MPSSE IC
Datasheet
Version 2.4
Document No.: FT_000060 Clearance No.: FTDI#78
In this case both channel A and channel C are configured as UART operating at TTL levels and a level
converter device (full duplex RS485 transceiver) is used to convert the TTL level signals from the FT4232H
to RS422 levels. The PWREN# signal is used to power down the level shifters such that they operate in a
low quiescent current when the USB interface is in suspend mode.
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.
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