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User Manual
Piccolo Range
8. Digital Communications
Digital Communications (or ‘comms’ for short) allows the controller to communicate with a PC or a networked
computer system.
This product conforms to MODBUS RTU protocol a full description of which can be found on www.modbus.org.
Two ports are available:-
1. An EIA232 (formerly RS232) configuration port - intended to communicate with a system to download the
instrument parameters and to perform manufacturing tests and calibration
2. an optional EIA485 (formally RS485) port on terminals HD, HE and HF - intended for field communications
using, for example, a PC running a SCADA package.
The two interfaces cannot operate at the same time.
For a further description of digital communications protocols (Modbus RTU) refer to the Communications Manual,
part number HA026230, available on www.eurotherm.co.uk.
Each parameter has its own unique Modbus address. A list of these is given at the end of this section.
8.1 Configuration Port
This is an EIA232 port intended only to be used for configuring the instrument using a configuration clip and iTools,
see section 10.2.1.
Do not use this port for any other purpose.
8.2 EIA485 Field Communications Port
To use EIA485, buffer the EIA232 port of the PC with a suitable EIA232/EIA485 converter. The Eurotherm Controls
KD485 Communications Adapter unit is recommended for this purpose. The use of a EIA485 board built into the
computer is not recommended since this board may not be isolated, which may cause noise problems, and the RX
terminals may not be biased correctly for this application.
To construct a cable for EIA485 operation use a screened cable with one (EIA485) twisted pair plus a separate core
for common. Although common or screen connections are not necessary, their use will significantly improve noise
immunity.
The terminals used for EIA485 digital communications are listed in the table below.
Standard
Cable Colour
PC Function *
Instrument
Terminal
Instrument
Function
White Receive, RX+ HF (B) or (B+) Transmit, TX
Red Transmit, TX+ HE (A) or (A+) Receive, RX
Green Common HD Common
Screen Ground
* These are the functions normally assigned to socket pins. Please refer to your PC manual.
See section 2.14 for wiring diagrams.
!
Warning. The Piccolo Range has a limited number of writes to EEPROM. Please ensure that parameters
which do not require updating on a regular basis (for example, setpoints, alarm trip levels, hysteresis, etc) are only
written to when a change in the parameter value occurs. Failure to do this could result in permanent damage to
the internal EEPROM.
See also the section 8.4.
78 Part No HA031260 Issue 1 May -12