AMG Systems Ltd. reserves the right to make changes to this
document without notice. The information herein is believed to
be accurate. No responsibility is assumed by AMG for its use.
Page 7 of 12
AMG5514A5B9 Instruction Sheet
D17370-00.doc
Data and Alarm Channel Configuration
The
AMG5514A5B9
transmit unit sends and receives data to/from an
AMG5513A5B9
or rackmount
equivalent
AMG5513A5B9R
transmit unit. The physical data interface RS-485, RS-422 or RS-232 is
selectable by the user with the slide switch mounted on the main PCB inside the enclosure.
Two bi-directional alarms are also provided. Each alarm input is typically connected to a contact
closure switch. An alarm output can receive an on/off signal from an
AMG5513A5B9
and is typically
used to convey contact closure status.
Data Channel Configuration
Each low speed data channel provides an RS-232, RS-422 (full duplex, four wire) or RS-485 (half
duplex, two wire) interface defined by the corresponding mode switch inside the enclosure. Every data
channel as shipped from the factory is set up for RS-485 operation unless otherwise requested.
The data input for both the RS-485 and the RS-422 modes detects a tri-state input condition by
monitoring the differential voltage level across the input. A differential level below 600mV positive or
negative will be detected as a tri-state condition. A level above 600mV positive or negative will be
detected as a logic 1 or logic 0 respectively. It is important therefore to terminate the RS-485 bus or
the RS-422 input bus using 120Ω if a pre-bias is present on the RS-485 or RS-422 bus.
A large number of third party equipment manufacturers apply a pre-bias on their RS-485 bus. This pre-
bias is applied by pulling one arm of the RS-485 bus high (+5 volts) and the other arm low (0 volts)
using high value resistors within the third party equipment. In order to ensure that the AMG equipment
detects a tri-state condition, then these resistors should have a value above 5kΩ. If the third party
bias resistors are less the 750Ω the bus can be multiple terminated as required to ensure that a tri-
state level is detected.
