Northern Design MultiCube Series Instruction Manual

MultiCube Series Meters
Simple Guide To RS485 Connection
This document is intended as a first approach to getting Modbus going from a PC running windows to a
Northern Design MultiCube Series meter. This merely proves the connection and provides confidence to
move on to longer cables multi-dropping and setting up SCADA software etc. A more comprehensive
document is available which covers some of the more advanced issues such as cabling, termination
resistors etc.
Setting Up
Use a short wire length from the PC to a single meter for convenience. Only the auxiliary mains supply is
required to the meter to test the communications link.
ENSURE ALL MAINS WIRES AND LIVE CONDUCTIVE PARTS ARE INSULTATED FULLY
TO PREVENT ELECTRIC SHOCK DURING THE TEST
READ THE INSTRUCTION MANUAL FOR THE METER FOR RELEVANT SAFETY
INFORMATION
RS232 – RS485(422) Converters
This plugs into the RS232 serial comms port of your PC (eg COM1) and converts the signals to RS485
compatible with the Cube meter communications port.
Ideally the converter should have the following features:
•Automatic direction turnaround (no RTS control required)
•Baud rate 4800 - 19200 (or greater)
•Baud rate select automatic (No need for DIP switches)
Northern Design use a B&B Electronics RS232 – RS485 converter model number 485DRJ. This note
provides connection details via this device only. We recommend use of this converter for ease of use.
NOTE: If your chosen converter requires RTS control much of the Windows software available for
MODBUS (including ND Busker) communications will not be reliable. For this type of
converter we recommend only RS422 connection (refer to operating manual) in an attempt
to create a reliable system.
RS485 Connections
The RS485(422) side of converters can often be connected to RS485 or RS422 systems alike. We
recommend the use of RS485 connection for simplicity and to reduce the number of cables pairs
required. The Modbus protocol is half-duplex which in essence means we only need a single pair for
transmission/reception of data. Most converters require external link wires at the converter to parallel
up the transmit/receive pairs of RS422 thus ending up with RS485.
Connection between the B&B Converter and the Cube meters is as follows:
RS485 Converter Cube Internal Comms Cube Retro-Fit Comms
(V1.08 & Earlier only)
Link RDB(+) and TDB(+) PIN 28 LINK 27-29
Link RDA(-) and TDA(-) PIN 27 LINK 28-30
GND – GND PIN 26 PIN 26

GETTING COMMS GOING NOV 2007.DOC © Northern Design (Electronics) Ltd 8 December 2007 Page 2 of 2
Northern Desi
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n (Electronics) Ltd, Bolton Road, BRADFORD BD3 0QW, UK
Tel: [phone] Fax: [phone] E-mail: [e-mail] www.ndmeter.co.uk
Test Software
Northern Design provides a Cube series MODBUS test program “Busker”, which is simple to
install/use running under Microsoft windows. We recommend this software to test the system
before setting up and installing proprietary software.
Busker is available as a free download from www.ndmeter.co.uk
Program Settings
Enter the programming mode of the Cube series meter and check/set the baud rate and Modbus address
for the meter. Take a note of the settings.
In Busker select OPTIONS -> PC COMMS from the menu and apply the following settings:
The user Address should match the Meter ID set in the programming menu.
The PC baud must match the baud rate set in the meter programming menu.
The PC Port determines which physical port on the PC to connect the RS232/485 converter.
If all goes well the Status bar at the bottom of the main Busker window indicates the number of Modbus
commands sent to the meter and the number of errors in the transmit/receive process. Pressing the
“Reset Stats” button at the top right of the window resets these numbers to zero. This facility may be
useful when commissioning the validity of the setup when the system is more complex.
Comms LEDs
If all is not well, the Cube series meters use diagnostic LEDs to aid in the fault finding of a
communications link. The function of these is described in the user manual for the communications
option of the meter.
Applies to the Following Products
Product Firmware Notes
MultiCube Internal Comms All Versions
MultiCube Option Unit V1.08 & Earlier Later versions of the MultiCube are not compatible
with Option Units
kWh Cube Internal Comms All Versions