General Specification Electrical Function gmw3110 General Motors Local Area Network Enhanced Diagnostic Test Mode Specification

GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 52 of 336 
The P2
CT
timer shall initially be started by the application layer of the tester after the successful transmission of 
the request message which is indicated by the network layer (N_USData.con). The P2
CT
timer shall be 
restarted by the application layer of the tester each time the network layer provides an indication, provided that 
the responses are associated with the corresponding request message for any of the following conditions: 

Receipt of a single frame USDT response message (N_USData.ind with length 
≤ 7, response messages 
always use normal addressing). 

Receipt of the first frame of a multiple frame USDT response message (N_USData_FF.ind,). 

Receipt of the first (or only) UUDT response message from service $AA or $A9 response message 
(N_UUData.ind, only the first UUDT message of a service $AA or $A9 response message shall restart 
P2
CT
). 
If the tester does NOT know the number of responding ECUs to a functional request the following handling 
applies: 

The tester shall wait for a P2
CT
timeout, and 

For services other than $AA and $A9, all USDT multi-frame response messages must be completely 
received, and 

For services $AA and $A9, depending on the sub-level parameter value, the tester either has to wait for 
the completion of all expected UUDT response messages, or only the first UUDT response message 
(reference services $AA and $A9). 
Note:
If the tester sends a functionally addressed request message which results in either multiple ECUs 
sending multi-frame USDT responses or multiple single frame UUDT responses, then the tester must pick an 
appropriate value for P2
CTmax
which allows all ECUs to have sufficient time to gain access to the bus. 
If the tester knows the number of responding ECUs the following handling applies: 
The tester should not wait for a P2
CT
timeout, but 

For services other than $AA and $A9, all USDT multi-frame response messages must be completely 
received, and 

For services $AA and $A9, depending on the sub-level parameter value, the tester either has to wait for 
the completion of all expected UUDT response messages, or only the first UUDT response message 
(reference services $AA and $A9). 
In both above listed cases the application layer has to keep track of the response messages following the 
request message. 
The tester implementation of P2
CT
as described assumes that the tester has implemented the network layer 
and utilizes the service primitives that it provides. The network layer of the tester provides an indication to the 
application layer each time any of the following occurs: 

The first frame of a multi-frame response is received (N_USData_FF.ind). 

The last consecutive frame of a multi-frame response message is received (N_USData.ind). 

A SingleFrame response is received (N_USData.ind with length 
≤ 7). See Figure 19. 

An error condition is detected by the network layer (N_USData.ind with a negative result code). 

A UUDT diagnostic response is received (N_UUData.ind). See Figure 21. 
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