Figure 46: RS422 Reference Schematic
2.15.2.3 RS485 Reference Schematics
The RS485 interface is a half-duplex serial interface with differential pair signals. Instead of two
differential pair wires (RS422), only one pair is used for transmitting and receiving the data. The
bus allows Multi-Point connections. Since the transceiver needs to be set either in the transmitting
or receiving mode, an additional control signal is required. It is recommended to use the RTS signal
of the corresponding UART interface. The RTS signal is only available on the UART1 and UART2 as
Apalis standard interface. The schematic shown below inverts the RTS signal for the data enable
input of the transceiver. Some modules allow inverting the signal in software, but it is
recommended to keep the inverter circuit in in the RTS signal in order to maintain compatibility
with different modules and drivers provided by Toradex. For some applications, it is desirable that
the UART controller does not see the TX message on its RX pins (echo of the sent message). In this
case, the receive enable pin (RE#) can be driven as well with the RTS signal. This turns off the RX
output buffer during sending a message.
Like the RS422, the RS485 specification does not describe a standard connector. The reference
schematic shown below uses a DE-9 connector which may have a different pin-out compared to
some peripheral devices.
Figure 47: RS485 Reference Schematic
2.15.2.4 IrDA Reference Schematics
IrDA is an optical wireless communication interface. There are different physical layer modulation
schemes available. Make sure that you check which modes are supported by a specific Apalis
module and the peripheral devices.
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