RS–422
RS–422 is typically point to point configuration. RS–422 is also specified for multi-
drop (party-line) applications where only one driver is connected to, and transmits
on, a “bus” of up to 10 receivers. The device at the end of an RS–422 network must
be terminated. The 5266 optionally terminates with a 100 ohm resistor. Refer to
table 4–3. Figure 4–3 shows a typical RS–422 four-wire interface circuit.
The RTS* signal is used to control the transmitter and receiver in RS–422 mode.
The RTS* signal is controlled by the Modem Control Register bit 1 (MCR[1], which
is offset 0x04 from the UART base address). Writing MCR[1] to 0 (default state)
sets RTS* to an inactive state (RTS* = logic high) which ENABLES both the RS–
422 Transmitter and Receiver. Writing MCR[1] to 1 sets RTS* to an active state
(RTS* = logic low) which DISABLES both the RS–422 Transmitter and Receiver.
Figure 4–3
Typical RS–422 four-wire interface circuit
Receiver
Xmitter
100
Ω
100
Ω
TX –
RX +
TX +
RX –
Gnd
100
Ω
Receiver
Xmitter
100
Ω
RX –
TX +
TX –
RX +
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