Monarch Instrument DC6000 - Manual (Page 101)

Section 6 - Communication
I.
Page 93
1/06/2012 REV 1.10.2
6.3.2 Modbus Server
The recorder supports Modbus TM RTU (Remote Terminal Unit) over Ethernet and optional RS232/RS485
interfaces.
An RS485 interface will support up to 64 Data Recorders linked to a single computer. Each of the Recorders will
be identified by a unique unit address (programmed under System Settings -
Modbus ). This address is set at 1 to
256 and must be different from any other recorder on the loop. Similarly if using the RS485 serial port the baud
rate must be set to match the system
– 9600 to 115,200 baud. Data Bits – 8, Parity – None, Stop Bits – 1. Flow
control if applicable should be RTS always. The RS232 interface may be used to communicate with a single
recorder.
Modbus over Ethernet (sometimes referred to as Modbus TCP) is supported through Port 502. In this case you
need to know the remote device IP address which can be read from the
System Information screen. The IP
address should static and is set up under Network Setting (Section 5.7.7)
Note that Modbus ASCII is not supported and this recorder supports a minimal subset of registers and is read only.
All data is read from holding registers using Function 03.
All Modbus registers are 2 bytes = 1 word. Status is in a single 16 bit register (Word) while Data is in two
consecutive registers (32 bit total
– using default Modbus byte order with first word low) – the data is in floating
point format.
The physical connection details are shown in Section 2
– Isolated Serial Option .
6.3.2.1 Modbus Status Registers
The Status Registers Are 16 bit Integers in the form of two bytes as follows (Low Byte = Bits 0 through 7).
When the bit is a “1” the condition is true. There is one register for each point or channel and the registers start
at number 3056. So Register no. 3056 is Channel 1 status, Register 3057 is Channel 2 status through Register
3071 which is Channel 18 status. These Registers are read only and are accessed using Function 4.
6.3.2.2 Modbus Data Registers
The Data Registers hold the current floating point value for each of the 18 data points (Channels) as IEEE
floating point numbers which require 4 bytes (2 words) as shown below. They are in the format
S
ign Bit
E
xponent
(+127 biased)
M
antissa
(Extra implied 1 bit)
1 bit 8 bits 23 bits
Bit 15 - 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Not
Used
0 or 1 0 or 1 0 or 1 0 or 1 0 or 1
Not
Used
Not
Used
0 or 1
Alarm 5 Alarm 4 Alarm 3 Alarm 2 Alarm 1
Any
Alarm
Byte 0 Byte 1 Byte 2 Byte 3
SEEEEEEE EMMMMMMM MMMMMMMM MMMMMMMM
High Word Low Word