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Proton Products InteliSENS DG2030 Diameter Gauge Instruction Manual (Issue 1a)
M
ODBUS PARAMETER ACCESS PROTOCOL
This protocol provides access to individual parameters or blocks of parameters and is typically used in
a production environment where the Proton Products instrument is connected to a computer, Modbus
connected PLC or similar device.
The parameters consist of 16-bit words (DW) and are divided into input and output groups:
•
Input parameters may be read from and written to and are used to configure the instrument.
•
Output parameters are read only and provide access to instrument status and measurement
data.
1 word (DW) consists of 2 bytes
1 byte consists of 8 bits
4 bits are expressed by 1 hexadecimal digit (0-9, A-F)
Proton Products instruments use the following Modbus format:
Modbus format
RTU (Remote Terminal Unit)
Error check
CRC (Cyclic Redundancy Check)
The Modbus RTU frame format is as follows:
Modbus RTU frame format
Name
Length
Function
Start
> 3.5 characters >3.5 characters of silence
Address
1-byte
Slave (instrument) Modbus address
*
Function 1-byte
Modbus function code determines read or write operation
*
Data
Multiple bytes
Length and data dependent on function
*
CRC
2-bytes
Cyclic Redundancy Check for errors (not required for Modbus TCP)
+
End
> 3.5 characters >3.5 characters of silence
+
Please refer to Modbus Protocol Standards documentation for the CRC error check field calculation. For Modbus protocol
communications over TCP/IP networks via the Ethernet port (also known as
Modbus TCP
), the CRC error check field is not
required as error checking is handled by the TCP/IP protocol.
For brevity, only the fields marked * are shown in the subsequent examples.
Proton Products instruments support the following Modbus functions:
Modbus function
Instrument operation
Code
Name
Dec Hex
03
03
Read Holding Registers
Read data from a block of consecutive
input
parameters.
06
06
Preset Single Register
Write data to a single
input
parameter.
16
10
Preset Multiple Registers
Write data to a block of consecutive
input
parameters.
04
04
Read Input Registers
Read data from a block of consecutive
output
parameters.
For Modbus protocol communications via the RS-232 serial port, the RS-232 data format is:
Number of data bits
Parity
Number of stop bits
Flow control
Default baud rate
8
None
1
None
115200 bit / s
