A 42
3
Modbus RTU Protocol
From firmware version 1.05.00 and up is it possible to use the protocol
Modbus RTU (Remote Terminal Unit) for data retrieval (alternatively to
SCTM / IEC 60870-5-102).
3.1
Telegram processing
The following rules define the protocol for information transfer between a
Modbus MASTER and the DLX:
•
The DLX supports only the “Modbus RTU mode of transmission”: Read
Holding Registers.
•
Transmission settings: 8, N, 1 (1 start bit, 8 data bits, no parity, 1 stop bit).
•
All communications on the network or bus conform to a MASTER/SLAVE
scheme. In this scheme, information and data is transferred between a
Modbus MASTER device (e.g. SIGLON AMR Software) and up to 32
SLAVE devices (DLX).
•
The MASTER initiates and controls all information transfer on the commu-
nications loop.
•
A SLAVE device (DLX) never initiates a communications sequence.
•
All communications activity on the loop occurs in the form of “PACKETS”. A
packet is a serial string of 8-bit bytes. The maximum number of bytes con-
tained within one packet is 255.
•
All packets transmitted by a MASTER are REQUESTS. All packets trans-
mitted by a DLX are RESPONSES.
•
At most one DLX can respond to a single request from a MASTER.
3.2
Telegram structure
Every Modbus packet consists of four fields (Request := eight bytes):
•
Slave Address Field: one byte between 1 and F7
Hex
; (:= 1 to 247
Dec
)
•
Function Field: one byte (:= 3 / fix, Read Holding Registers)
→
Modbus address := device address – 40001
•
Data Field:
Request: four bytes (start register: 2 bytes, # of reg.: 2 bytes)
Response: x bytes (counter: 1 byte, n registers: 2*n bytes)
•
Error Check Field (Checksum): two bytes, a 16-bit Cyclic Redundancy
Check (CRC-16)
Example: Address: 1 / Start register: 102
Dec
(00 66
Hex
) / # of registers: 2 (32-bit)
Request:
Addr. Function
Start register
# of Register
CRC
01
03
00
66
00
02
65
CB
Response:
Addr. Function Counter
Register 1
Register 2
CRC
01
03
04
00
00
00
12
49
3E
Value = 18 (00 00 00 12
Hex
)
Summary of Contents for DLX
Page 9: ...9 1 Scope of Application 1 1 Application environment Figure 1 Application environment...
Page 42: ...42 4 2 Installation diagram Figure 13 Dimensions of mounting points...
Page 54: ...54 7 Menus 7 1 Flow diagram Figure 24 Flow diagram of menus...
Page 110: ...Subject to change without notice...
Page 111: ...E116012215052 Appendix A Data Retrieval Protocols...
Page 112: ...A 2...
Page 156: ...Subject to change without notice...
Page 157: ...E116012215052 Appendix B Table Addresses...
Page 158: ...B 2...
Page 170: ...Subject to change without notice...
Page 171: ...E116012215052 Appendix C List of Parameters and Constants...
Page 172: ...C 2...
Page 178: ...Subject to change without notice...