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

Tester P3
C
 timeout < P3
Cnom
 
≤ ECU P3
C
 timeout < P3
Cmax
 
P3
Cmax
is equal to P3
Cnom
plus a 2% tolerance. Further references to P3
C
within this specification are 
references to the nominal value of P3
C
unless a subscript is included (e.g. P3
Cmax
). Refer to the TesterPresent 
service description in this specification for more information about the TesterPresent timeout. 
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GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 62 of 336 
Figure 29: P3
C
 Timing Parameter Definition and Handling of the TesterPresent Logic 
In Figure 29, the tester has set up its P3
C
timer to a value less than the P3
C
value of the ECU. Therefore, the 
P3
C
timer of the tester times out earlier than the ECU P3
C
which forces the tester to transmit its functionally 
addressed TesterPresent service request message. See Table 34. 
Table 34: P3
C
 Start and Reset Definition for the Tester and ECU 
P3
C
 Start 
P3
C
 Reset 
Tester 
Confirmation from the Network Layer that a 
service has been successfully transmitted that 
requires the tester to send a TesterPresent 
message in order to keep the service 
functionality active. 
A P3
C
timeout triggers the reset of the P3
C
timer 
and the transmission of the TesterPresent 
request message. 
ECU 
When the ECU has received a diagnostic 
message and the application has determined that 
the service requested requires the activation of 
the P3
C
timer. 
See pseudo code of the diagnostic services in 
this specification. 
When the ECU has received a diagnostic 
message and the application has determined that 
the service requested is the TesterPresent 
service. 
See pseudo code of the TesterPresent service. 
The tester implementation of P3
C
assumes that the tester has implemented the network layer and utilizes the 
service primitives that it provides. The network layer of the tester provides a confirmation to the application 
layer each time any of the following occurs: 

A single frame request is transmitted (N_USData.con). 

The last consecutive frame of a multi-frame request message is transmitted (N_USData.con). 

An error indication is detected by the network layer (N_USData.con with a negative result code).