Modbus Communication; Overview Of Modbus Rtu And Tcp Communication Modbus Tcp Instructions V13 - Siemens S7-1200 System Manual
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- Operating instructions manual (132 pages) ,
- Programming manualline (74 pages) ,
- Manual (46 pages)
Table of Contents
12.5
Modbus communication
12.5.1
Overview of Modbus RTU and TCP communication Modbus TCP instructions
V13
Modbus function codes
● A CPU operating as a Modbus RTU master (or Modbus TCP client) can read/write both
● A CPU operating as a Modbus RTU slave (or Modbus TCP server) allows a supervisory
If an attacker can physically access your networks, the attacker can possibly read and write
data.
The TIA Portal, the CPU, and HMIs (except HMIs using GET/PUT) use secure
communication that protects against replay and "man-in-the-middle" attacks. Once
communication is enabled, the exchange of signed messages takes place in clear text
which allows an attacker to read data, but protects against unauthorized writing of data.
The TIA Portal, not the communication process, encrypts the data of know-how protected
blocks.
All other forms of communication (I/O exchange through PROFIBUS, PROFINET, AS-i, or
other I/O bus, GET/PUT, T-Block, and communication modules (CM)) have no security
features. You must protect these forms of communication by limiting physical access. If an
attacker can physically access your networks utilizing these forms of communication, the
attacker can possibly read and write data.
For security information and recommendations, please see our "Operational Guidelines for
Industrial Security"
security/Documents/operational_guidelines_industrial_security_en.pdf) in the Siemens
Service and Support site.
Table 12- 45 Read data functions: Read remote I/O and program data
Modbus function code
01
02
03
04
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
data and I/O states in a remote Modbus RTU slave (or Modbus TCP server). Remote
data can be read and then processed in your program logic.
device to read/write both data and I/O states in CPU memory. A RTU master (or Modbus
TCP client) can write new values into slaver/server CPU memory, that are available for
your program logic.
WARNING
(http://www.industry.siemens.com/topics/global/en/industrial-
Communication processor and Modbus TCP
Read slave (server) functions - standard addressing
Read output bits: 1 to 2000 bits per request
Read input bits: 1 to 2000 bits per request
Read Holding registers: 1 to 125 words per request
Read input words: 1 to 125 words per request
12.5 Modbus communication
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