SS1000 Operator’s Manual
4
–
0
1
-
9
2
-
4
A
.
v
e
r
9
7
0
2
0
-
0
0
0
9
4
2
1
standard communications protocol in industry, and is now the most commonly
available means of connecting industrial electronic devices. Modbus is used
extensively in leu of other communications protocols because it is openly
published and royalty-free, relatively easy to deploy, and capable of moving
raw bits or words without placing many restrictions on vendors.
Modbus enables communication between many devices connected to the same
network, for example, a supervisory computer with a remote terminal unit
(RTU) in supervisory control and data acquisition (SCADA) systems.
The SpectraSensors analyzer acts as a slave in a master/slave(s) network of
devices. It can receive queries from a master and send responses back using
either Gould Modbus RTU protocol or Daniel Extended Modbus RTU protocol.
Framing/Protocol
The transmission mode used to communicate is either Gould Modbus RTU or
Daniel Modbus RTU with port parameters 9600 (baud rate), 8 (data bits), 1
(stop bit), no (parity), and none (flow control/handshake).
The transmission mode is set by the user via the
Modbus Mode
parameter.
See
“To change parameters in Mode 2”
on page 3-6. Note that the generic
serial output (HyperTerminal) is disabled if either Gould or Daniel Modbus is
selected.
Functions
Available functions are 0x03 (read holding registers), 0x06 (write to a single
register), 0x16 (write to multiple registers), and 0x43 (read device
identification).
Addressing
The analyzer's Modbus slave node address can be in the range of 0-250 with
the default being 1. All analyzers will respond to an address of 0, so this
address can be used to interrogate a single unit when its address is unknown
or to determine its address.
See Table 4–1 on page 4–15 for register definitions for both Gould and Daniel
Modbus modes. Be aware that for Gould Modbus the table follows the
convention of identifying the register with an offset of 40001. For example, the
actual value transmitted in the starting register field of the command is the
listed register value minus 40001, e.g. register 47001 is addressed as 7000.
Reading/Writing in Daniel Modbus Mode
Daniel Modbus supports three types of registers: short integer, long integer and
floating point. Each “short integer” register is two bytes in length and will
contain an integer value. Each “long integer” register is four bytes in length and
will contain an integer value and each “floating point” register is four bytes in
length and will contain a floating point value.
UK Distibution by IMA Ltd
Tel: +44 (0)1943 878877 Email: [email protected] Web: www.ima.co.uk