100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
HA028910
Issue 13 Sep 16
User Guide
Page 154
4.3.16 Master comms
INTRODUCTION
This option allows the unit to be used as a Modbus Master unit, as well as a Modbus Slave. The instru-
ment can communicate using the Ethernet (RJ45) connection, or by means of one of the serial communi-
cations ports (if fi tted - see
section 4.3.15
for details) or both simultaneously.
Master Confi guration consists of entering a Modbus Address, and, for Ethernet connection, an IP ad-
dress or DNS path name for each of the available remote devices which are to be used as slaves. The
confi guration also allows three different priority intervals to be entered, and read/write parameters can
be confi gured to be accessed at one of these three rates.
The unit comes complete with a number of ‘Profi les’ for known instruments. This allows it to ‘recognise’
an instrument as a slave type, and simplifi es the read/write process for ‘known’ instruments, by present-
ing commonly used Parameters by name. Other parameters can be accessed by entering the relevant
register’s address. The unit will also communicate with ‘third party’ instruments, but in such a case, the
user has to defi ne the required read/write register addresses derived from data supplied by the manu-
facturer of the instrument.
Once the remote unit has been recognised by the master, the master and slave units can be confi gured
to carry out the following:
1. By setting a master input channel to: Type = ‘Master Comms’, selected parameters can be read by
the master from a selected slave. This master channel can then be included in display groups, can
have alarm setpoints, run jobs etc., independently of the original channel. In a similar way, maths
functions can be read by setting a master Maths channel to: Function = ‘Master Comms’.
2. The ‘Demand Write’ feature can write values to a selected parameter in a selected slave, as a one-
shot update. Demand Writes can be initiated by operator action, or they can be initiated by job ac-
tion or (if the User Screens option is fi tted), by Operator Key action.
3. For slaves whose input and/or maths channels can be set to ‘Modbus Comms Input’, the master’s
‘Output channels’ feature can copy master input or maths channels to a selected slave, as a continu-
ous process.
Notes
1. If reading from or writing to more than one instrument, it is recommended that some thought
be given to instrument and point descriptors, as confusion can easily arise. This is particularly
true if Bridge is connected to a master which has several slaves attached.
2. If ‘Link error’ occurs whilst connected to a Modbus slave, the slave’s delay parameter (if any)
should be enabled. If no such parameter is available, the slave’s manufacturer should be con-
tacted for advice.
An example confi guration is given later in this section showing how to set up a master unit to read inputs
from two slaves, and to re-write one of these channels to a third slave.
