[UDS unified diagnostic service] III. application layer protocol (1)

3、 ... and 、 Application layer protocol （1）

Where the application layer is located

Next , Start to explain the application layer protocol .

1. Typical service structure

（1） The client sends , The server receives and replies

（2） The client sends , The server receives

2. Application layer protocol

（1） Application layer protocol data unit （A_PDU,Application_Protocal Data Unit）

（2） Application layer protocol control information （A_PCI,Application_Protocal Control Information）

3. request （Client issue ） And response （Server reply ） Example

A term is used to explain ：

Before giving a formal example , You can learn the following , For better understanding ：
Cvt：Convention practice , convention , Appointment
C：Conditional The conditional , Whether to use depends on other parameters . request / The response message is marked as “C" The parameter of appears only under the specified conditions ;
M：Mandatory mandatory sex . request / The response message table is marked as “M" The parameter for always exists ;
U：User(optional) user ( Selectable ). request / The response message table is marked as "U" The parameters of are provided according to the dynamic use of the manufacturer .
S： Force the selection of... From the parameter list （ Enumeration type ）

(1) request （ No tape function ）A_PDU

(2) request （ Tape function ）A_PDU

(3) Positive response A_PDU

(4) Negative response A_PDU（NR,Negative Response）

4. Negative response code NRC（Negative Response Code）

Only the most common ones are listed below ：