wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

47-12 Industrial Communication Systems
11 Code
Tool related data
CRC
Safety-related parameter
Error code
Transaction ID
Source safe address
Command ID
(a)
Byte
1 3 1
1 Max. 34
2
11 Code
Tool related data
CRC
Safety-related parameter
Transaction ID
Destination safe address
Command ID
(b)
Byte
1 3 1
Max. 35
2
FIGURE 47.11 (a) Request message of SafetyLon management tool. (b) Response message of SafetyLon
management tool.
The SLL software architecture consists of two interfaces and one application. An API handles the connection
to LNS Object Server, another API is the interface for the SLA to the SLL. The handling of LNS
Object Server is described in the Echelon guidelines of the LNS application developer’s kit [15].
From the implementation point of view, the SLL is divided into three parts. The SLL is used by the client.
It provides functions to configure a safe node. It uses the SafetyLon message part to build and check the
management messages. The message is sent by the SLL to the safe node. The current configuration of a
safe node including the safe address is stored in the SafetyLon database. It manages and stores the safe
addresses. Additionally, it saves all configuration information.
The SafetyLon management tool supports the three-step process explained in Section 47.3 applied to
configure and commission a node. It uses explicit messages and a defined message structure (cf. Figure
47.11) different from the one used to exchange sensor or actuator data among nodes. Therefore, it can
be explicitly distinguished between a message sent from a management unit and messages sent from a
SafetyLon node, respectively.
The management message is embedded into the payload of an explicit message. It starts with a
Command ID specifying the command to be carried out at node side (e.g., assign a safe address to a
network variable). The destination safe address (SADR) is a unique safe address of the node that shall be
addressed. The transaction ID is a consecutive number that makes a correlation of request and response
possible. Data are a configuration parameter such as a safe address of a network variable. CRC16, finally,
is a 2 byte CRC appended to the message to ensure data integrity. In case of a response message, an additional
byte is included: an error byte that is set by the node (e.g., the network variable is not available).
© 2011 by Taylor and Francis Group, LLC