Modbus Clause Samples

Modbus. MODBUS is an application-layer messaging protocol, positioned at level 7 of the OSI model. It provides client/server communication between devices connected on different types of buses or networks. The de facto industrial serial standard since 1979, MODBUS continues to enable millions of automation devices to communicate. Today, support for the simple and elegant structure of MODBUS continues to grow. The Internet community can access MODBUS at a reserved system port 502 on the TCP/IP stack. MODBUS is a request/reply protocol and offers services specified by function codes. MODBUS function codes are elements of MODBUS request/reply PDUs. This protocol specification document describes the function codes used within the framework of MODBUS transactions.

Modbus. While the serial Modbus RTU protocol does not provide any security functions [20], the principal security mechanism for Modbus TCP is the Access Control Module that provides authorisation based on the source IP address [21]. This is not considered state-of-the-art, as the fact that IP addresses can be easily spoofed is known for a long time [22]. The threat model therefore considers both protocols as having no security set (see Table 6). The Modbus Organization has reacted to the higher security demand to an IP-connected world and issued a MODBUS/TCP Security protocol specification that relies on Transport Layer Security (TLS) [23, 24] to secure communications [25]. In contrast to TLS, Modbus TCP/IP Secure mandates client (source) authentication also, therefore the threat model reflects that.

Modbus. (Other) Ups Junction Box QMT Local PC QBT Access Control Router Satellite Switch Satellite Aerial Anti-intrusion + Panels theft Local PC Server Technical Assistance Back-up unity Plant n Plant 1 Server WEB Plant 2 Server Server Technical Assistance Semi-automatic procedures for solving of errors and anomaly Electronic Squad Trouble Ticketing Handling First Aid Mechanics Squad Electricians Squad [Certain terms translated from Italian] Annex 8: Safety Costs

Modbus. Usage of Modbus TCP/IP Security (4.1.5) or Segregation measures (4. 1.1 except for shared media such as wireless communications). Table 31 gives a structured overview of the requirements for the Modbus protocol. Communications Segregation* 4.1.1 Enforce Modbus TCP/IP Security with encryption* 4.1.3

Modbus. Intrinsically safe cards and barriers are to be used as required for hazardous areas. A Safety Instrumented System must be used for emergency shutdown and monitoring/control of safety-critical parameters in the Plant. The SIS shall be designed in accordance with IEC 61508 and IEC 61511. There should be an interface between the BPCS and the SIS for information exchange as to allow indication and status of all critical parameters and functions handled in the SIS directly to the operator. The hardware used to create the SIS shall fulfill and comply with all relevant standards (such as IEC 61508) accepted by the industrial community. Equipment included in the system shall be chosen with appropriate SIL-classification as necessary. The software configuration must be performed by competent engineers. The basic design of the SIS is founded on different methods of risk assessment analyses, as well as feedback and experience from previous Plant designs. If required, a separate and additional risk assessment will be performed for each individual system. This is done in order to guarantee that all client-specific issues are covered in the design, including local regulations which might deviate from general international standard All vital Process parameters are to be monitored through the control system. Hence, electronic transmitters are to be used for both measurement and control. The major portion of instruments should be equipped with a local indicator or display in order to provide local indication in the Plant. The use of bus-systems such as Foundation Fieldbus or Profibus PA is recommended as the amount of information available from the instruments is extensive. This information can be used for e.g. preventive maintenance, enhanced performance and other cost saving and production improving functions for the Plant. Control and remote On/Off-valves are to be pneumatically operated. Some valves should have actual position feedback. It is recommended that all instrumentation located in hazardous areas are designed and approved according to valid ATEX-directives. Clean, oil-free and dry instrument air is to be supplied to different consumers within the process, mainly Control- and remote On/Off-valves, at a stable and suitable pressure according to vendor requirements. THE BUYER’s site will supply instrument air at approximately 90 psig and a maximum dew point of -20 oF. and has a back-up tank to allow safe shut-down of the Plant in case of a failure in the air sup...