Super Systems 3L Series - Manual (Page 41)

Series 3L Indicators
41
11.2.1 Broadcast Communications
Broadcast master communications, as a simple master,
allows the Series 3L indicator to send a single value to
any number of slave instruments. Modbus broadcast
using function code 6 (Write single value) must be
used. This allows the Series 3L to link with other
products, without the need for a supervisory PC, to
create a small system solution. The facility provides a
simple and precise alternative to analogue
retransmission.
The retransmitted parameter is Process Variable. The
indicator will cease broadcast when it receives a valid
request from a Modbus master.
!
Warning
When using broadcast master communications, bear in
mind that updated values are sent many times a
second. Before using this facility, check that the
instrument to which you wish to send values can accept
continuous writes. Note that the SSI Series 3L does
not accept continuous writes to the temperature
setpoint. Damage to the internal non-volatile
memory could result from the use of this function.
If in any doubt, contact the manufacturer of the
device in question for advice.
When using the 3L series indicator fitted with software
version 1.10 and greater, use the Remote Setpoint
variable at Modbus address 26 if you need to write to a
temperature setpoint. This has no write restrictions and
may also have a local trim value applied.
11.2.2 Broadcast Master Communications
The Series 3L broadcast master can be connected to
up to 31 slaves if no segment repeaters are used. If
repeaters are used to provide additional segments, 32
slaves are permitted in each new segment. The master
is configured by setting the ‘RETRAN’ parameter to
PV.
Once the function has been enabled, the instrument will
send this value out over the communications link every
control cycle (250ms).
Notes:-
1. The parameter being broadcast must be set to the
same decimal point resolution in both master and
slave instruments.
2. If any Modbus master, is connected to the port on
which the broadcast master is enabled, then the
broadcast is temporarily inhibited. It will restart
approximately 30 seconds after the master is
removed.
11.2.3 Wiring Connections
The Digital Communications module for use as a
master or slave uses terminals HD to HF.
EIA485 2-wire Connections
Connect A in the master to A of the slave
Connect B in the master to B of the slave
This is shown diagrammatically below
Series
3L
Master
Slave
1
Slave
2
Slave
31
Series 3L
Master
EIA485
B
A
Slave 1
EIA485
B
A
Com Com