Eurotech Appliances PXA270 RS485, Typical RS422 and RS485 connection

ZEUS Technical Manual Detailed hardware description

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

RS422 POINT-TO-POINT RS422 MULTI-DROP RS485 MULTI-DROP

Number of Wires	5	Number of Wires	5	Number of Wires	3
Transmitters Enabled	always	Transmitters Enabled	active RTS#	Transmitters Enabled	active RTS#
Receivers Enabled	always	Receivers Enabled	always	Receivers Enabled	always
Duplex Mode	full	Duplex Mode	full	Duplex Mode	half
RS485EN	LOW	RS485EN	LOW	RS485EN	HIGH

Only set U3_TERM# (U4_TERM#) at logic low if the ZEUS is at the end of the network.

© 2007 Eurotech Ltd Issue D 56