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

T
Eval
:
This delay is based on the required evaluation of the request message (check of the service identifier 
and evaluation, that the request message is correct). The figure above shows the earliest point in time 
when the application can queue its response message. 
The total transmit delay T
RESPONSE
is made up from the following components: 

T
R1
:
This is the delay within the ECU between the application queuing the response message and actually 
placing the first CAN frame of the response (SF or FF) in a transmit object of the CAN controller. 

T
R2
:
This is the delay based on arbitration with higher priority CAN frames which can occur before the 
frame is actually transmitted on the CAN bus. This delay varies based on the bus load and the priority of 
the response frame compared to the priority of CAN frames in the transmit objects of other ECUs. 

T
TX
:
This is the transmit time of a single CAN frame. This time depends on the baud rate of the GMLAN 
subnet where the CAN frame is transmitted, the number of data bytes in the frame, and the bit pattern 
which determines the number of stuff bits. 
Note:
The above described delays for the response message have to be considered in order to meet the P2
CE
timing requirements defined in this specification. T
R2
depends on the bus load and frame priorities. If no loss of 
arbitration occurs, this delay time is equal to 0. 
The reception delay (T
REQUEST
) is also applicable when receiving a service which requires a TesterPresent 
(activation of the P3
C
timer) or when receiving a TesterPresent message which resets the P3
C
timer. As 
defined in paragraph 6.2.4, an ECU shall not timeout later than P3
Cmax
. This allows the ECU a total tolerance of 
100 ms (2% of 5000 ms) for its P3
C
timer (P3
Cmax
= 5100 ms). The T
REQUEST
delays shall be comprehended 
within this 100 ms tolerance. 
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