Australian Monitor DMA1 - Manual (Page 28)

S E R I A L R S 4 8 5 C O M U N I C AT I O N
PA G E 2 8 A M I S - D M A 1 I N S TA L L AT I O N & O P E R AT I O N M A N U A L
9.1 RS485 communication
The DMA1 can be connected to a Crestron control system or similar via
RS485 serial connection.
Interference effects and induced noise on the serial line may cause anoma-
lous behaviour and possible damage to the DMA1 unit. To avoid this, take
the following precautions:
1. Do not let the serial cables transit the same conduits as power
cables or cables with elevated voltage. Maintain a safe distance of
at least 10 cm. between these cables
2. Connect the serial cable screen to the ground of one of the
RS485 devices (do not connect the screen at both ends)
3. Disconnect power from the DMA1 and control system before
wiring the serial control lines
The DMA1 supports up to 4 different RS485 modes of operation, accord-
ing to the RS485 electrical standard. This serial multipoint communication
supports the connection of up to 32 devices, with a maximum bus distance
of 50 metres.
The DMA1 devices connected to the RS485 bus can not autonomously begin
communication, but can respond to a specifi c request (command) from a
control system.
The RS485 connection parameters (speed, parity, check-sum, etc.) are set in
the confi guration fi le confi g.txt. (par. 9.2).
IMPORTANT!
• The internal electronics of DMA1 are not galvanically insulated
from the RS485 line; in case of short circuit or discharge to ground, it
is possible to damage not only the DMA1, but the control system to
which it is connected!
• The control system must remember to ignore the transmission
echo from the control system that is returned through the RS485
serial line.
IMPORTANT!
• To enable the serial port through the IN5/485A and IN6/485B
pins, remove the cover of the device and move the P1 and P2
jumpers, as indicated in the following fi gure.
• With an RS485 connection termination resistors must be applied
on both extremes of the serial line to avoid the generation of
stationary waves and to defi ne the impedance of the serial
line - even in absence of serial communications. The DMA1 features
internal termination resistors, enabled through a JP1 bridge jumper.
To deactivate the terminating resistors, remove the cover of the
device and remove the JP1 jumper indicated in the following fi gure.