Rs485 – Eurotech Appliances ZEUS PXA270 User Manual

Page 56

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

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

Transmitters Enabled

always

Receivers Enabled

always

Duplex Mode

full

RS485EN LOW

Number of Wires

Transmitters Enabled

active RTS#

Receivers Enabled

always

Duplex Mode

full

RS485EN LOW

Number of Wires

Transmitters Enabled

active RTS#

Receivers Enabled

always

Duplex Mode

half

RS485EN HIGH