ISO 20794-2:2020 pdf free.Road vehicles——Clock extension peripheral interface (CXPI)——Application layer.
5 Conventions
This document is based on the conventions discussed in the OSI Service Conventions as specified in
ISO/IEC 10731.
6 Introduction to application and application layer
6.1 Application properties
The application has the following properties:
— communication methods;
— message types;
— network management (optional wake-up, sleep);
— state management (state machine);
— measurement and/or control data; and
— error handling.
6.2 Application layer properties
The application layer has the following properties:
— message exchange;
— message structure; and
— service interface and parameters.
6.3 Message transmission
A message consists of a request field and a response field. The node that corresponds to a request identifier composed in the request field can transmit the response field.
6.4 Communication methods
Two communication methods are supported:
— Event-triggered method
Each node can request a request protected identifier field and response field based on an internal event occurrence.
— Polling method
The master node requests a request protected type identifier field (event request in polling method) to the lower OSI layers and then each node can transmit a request protected identifier field. The node corresponding to the request protected identifier field transmits the response field.
6.5 Message types
The application layer supports the following message types:
— request message field;
— response message field; and
— request sleep message field.
6.6 Error handling
The error handling is based on the following measures:
— CXPI network errors; and
— sequence count error (optional).
A message consists of a request protected type identifier field or a request protected identifier field and a response field (PDU). The request protected identifier field is transmitted by a node. The node that corresponds to the request protected identifier field value can request the response field (PDUJ to the lower OSI layers.There are two kinds of requests that the master node requests about the request protected identifier field and the request protected type identifier field. When the master node requests the request protected type identifier field (event request in polling method) to the lower OS! layers, each node can request the request protected identifier field. If multiple nodes request the request protected identifier field at the same time and the request protected identifier fields collide on CXPI network, a non-destructive arbitration takes place in the data link layer and the higher priority request protected identifier field is transmitted to the CXPI network. The node corresponding to the request protected identifier field requests the response field (PDU). The slave node oniy requests PDUs when it receives the request protection identifier field or request protected type identifier field from the master node. The slave node cannot request PDUs voluntarily.If the master node application is in polling method, then the master node shall periodically request a request protected type identifier field (event request in polling method) or a request protected identifier field, or both, to the lower OSI layers. The node corresponding to the request protected identifier field shall request the response field (A_PDU) including application measurement and/or control data.
Figure 4 shows an example of the polling method sequence. When the master node ‘1’ requests the periodic request protected identifier field PID ‘B’ to the lower OSI layers, each node can request the response field. In this example, node ‘2’ requests the response field PDU ‘B’.
Then an event occurs in node ‘3’. The master node ‘1’ requests a periodic request protected type identifier field (PTYPE) to the lower OSI layers, which allows all nodes to request a request protected identifier field. In this example, node ‘3’ requests a request protected identifier field PID ‘C’ followed by a response field PDU ‘C’.
The master node ‘1’ requests the periodic request protected identifier field PID ‘C’ to the lower OSI layers and node ‘3’ requests the response field PDU ‘C’.ISO 20794-2 pdf download.