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 8 of 12
AMG5904A966B9 Instruction Sheet
D22153-00.doc
Data and Alarm Channel Configuration
The
AMG5904A966B9G
receive unit sends and receives data to/from an
AMG5903A966B9
or
rackmount equivalent
AMG5903A966B9G
transmit unit. The 2 physical data interfaces RS-485, RS-
422 or RS-232 are individually selectable by the user with the slide switch mounted from the rear
panel.
There are also 8 bi-directional alarm inputs provided, each alarm input is typically connected to a
contact closure switch. Each alarm output can receive an on/off signal from an
AMG5903A966B9
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.
The system detects a tri-state input condition on the data channel bus when in RS-485 or RS-422
mode.
Data Interface Connections
Data Channel
Connector
Pin No.
RS-485
[switch bottom]
RS-422
[switch middle]
RS-232
[switch top]
1
IN/OUT - (B)
OUT - (B)
OUT
2
IN/OUT + (A)
OUT + (A)
3
GND
GND
GND
4
IN - (B)
5
IN + (A)
IN
Note: (A) or (B) in brackets in the above table refers to RS-485 / RS-422 data specification.
Data Channel Termination
The interface mode RS-232, RS-422 or RS-485 of each data port Data 1-4, is selected with the
corresponding external slide switch D1-D4. The actual number of data channels provided on the unit
depends upon the AMG model.
Internal 120Ω termination resistors across IN+ and IN- inputs may also be applied when in RS-422 or
RS-485 mode using internal DIP switches P0-P3 on the main PCB inside the enclosure. P0-P3 may
