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ZEUS Technical Manual Detailed hardware description
© 2007 Eurotech Ltd Issue D 56
RS485
This is a half-duplex interface that provides combined TX and RX signals (TX+/RX+
and TX-/RX-). A ground connection is also required for this interface. The maximum
cable length for this interface is the same as RS422 - 1200m (4000ft), but RS485
supports up to 32 transmitters and receivers on a single network. Only one transmitter
should be switched on at a time. The ZEUS uses the RTS# signal to control
transmission. When this signal is at logic 1, the driver is switched off and data can be
received from other devices. When the RTS# line is at logic 0, the driver is on. Any
data transmitted from the ZEUS is automatically echoed back to the receiver. This
enables the serial communications software to recognize that all data has been sent,
and disable the transmitter when required.
Typical RS422 and RS485 connection
Only set U3_TERM# (U4_TERM#) at logic low if the ZEUS is at the end of the
network.
RS485 MULTI-DROP RS422 POINT-TO-POINT RS422 MULTI-DROP
Number of Wires 5
Transmitters Enabled always
Receivers Enabled always
Duplex Mode full
RS485EN LOW
Number of Wires 5
Transmitters Enabled active RTS#
Receivers Enabled always
Duplex Mode full
RS485EN LOW
Number of Wires 3
Transmitters Enabled active RTS#
Receivers Enabled always
Duplex Mode half
RS485EN HIGH