SARAD GmbH
10
User Manual RTM1688-2 06-02-2019.docx
Version RTM1688-2 MODBUS
General information
A modified firmware is implemented in this version of the instrument which allows the
integration of the unit into MODBUS RTU (industrial standard) based networks. Because the
RTM1688-2 offers no native RS485 hardware interface, the instrument must be connected
to the bus lines through a commercial available RS232/RS485 converter. The converter must
support the automatic switch-over between the transfer directions. We recommend a
converter with optical-isolated RS485 data lines such as EXPERT EX9520R. The MODBUS
interface supports only the transmission of the recent readings. For all other functions the
SARAD standard protocol has to be used. The protocol frames are explained in detail by the
document “SARAD_MODBUS_Protocol”. The complete MODBUS Documentation can be
found in the internet under “modbus.org”.
In comparison with the standard instrument, for the MODBUS version the following
functions are skipped:
•
Protocol printing
•
Toggling of physical unis (US/SI) – only SI units are supported
•
Display of setup parameter on the instrument display
Selection of the transfer protocol, Addressing
To identify a instrument within a network, a unique address in the range of 1…250 must be
assigned. This address can be programmed into the instrument using the initialization
software “RadonScoutInit”. The edit field “RD:SWV WR:ADR” contains after loading the
configuration parameters (GET) the recently programmed firmware version. Now, the
desired address can be entered and transferred to the instrument (SET). Please note that the
parameters have to be read at first before uploading the new setting.
The requested transfer protocol can be chosen by the Toggle button of the RTM1688-2.
Keep the button down for four beeps and release it. After that, the actually used protocol is
shown at the display. a short keystroke toggles the available protocols. For configuration
purposes (e.g. setting the address), data download etc. the item “SARAD protocol” must be
selected. The items “MODBUS 9600bps” and “MODBUS 19200bps” select the MODBUS
protocol running a different bus speeds.
After selection of the protocol, the button must be pressed again for four beeps to come
back to the main menu.
Implemented MODBUS functions
Function code 0x03 (read holding register)
Valid register addresses are:
Register
Address
Register content
Number of
registers
Format
