Videotec EXDTRX3, Instruction Manual

Page: 15 / 124

EN - English - I
nstruc
tions manual
13
Terminals RX-485A and RX-485B which have the load
inserted, should be connected to terminals TX-485A
and TX-485B respectively of the preceding unit,
which also have the load inserted:
RS485
TX-
B
TX-
A
RX-
B
RX-
A
RS485
TX-
B
TX-
A
RX-
B
RX-
A
RS485
TX-
B
TX-
A
RX-
B
RX-
A
From previous
receiver
To next
receiver
Fig. 10
j For the connection in question (point-
to-point) faulty operation of one of the
receivers will switch off all the devices in
cascade.
6.2.11 More than one receiver per line,
connection with twisted pair cable
(multipoint connection)
All receivers connected to the same line should use
the same communication protocol RS485.
For each of the lines the following remarks are valid:
• Only one of the keyboards (that at one end of the
line) has the load inserted;
• Only one of the receivers (at the other end of the
line) has the load inserted;
• The total length of the line should not exceed
1200m.
6.2.10 Connecting more than one receiver
in cascade (point-to-point connection)
The receivers are able to regenerate the received
signal internally and retransmit it along a new
communication line to the subsequent receiver. Each
of the three sections of line (L1, L2, L3) is considered
independent, and connects only two devices
point-to-point, each with inserted load, over a
maximum distance of 1200m. The distance between
the keyboard and receiver D can therefore be up
to 3600m (1200m between keyboard and receiver
B, 1200m between receiver B and receiver C, and a
further 1200m between receiver C and receiver D, for
a total of 3600m).
C D B
A
EXPT EXPT
DCT
L2
L1
EXPT
EXDTRX3
EXDTRX324
EXDTRX3
EXDTRX324
EXDTRX3
EXDTRX324
L3
Fig. 09
The connection between the keyboard and the first
receiver must be carried out as illustrated in the
diagram in
Fig. 08, page 12 .