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 34 of 336 
Figure 4 gives an overview of the occurrence of the ISO 11898 and OSEK-COM service primitives during a 
request/response sequence, where the tester transmits a SingleFrame request message to a single ECU using 
the USDT protocol and the ECU responds with a multiple frame response message (two (2) 
ConsecutiveFrames) using the USDT protocol, too. 
Req_SF
Resp_FF
Resp_CF
FlowControl
Resp_CF
Physical Layer
Tester
ECU
N_USData.req
N_USData.ind
N_USData.req
N_USData_FF.ind
N_USData.con
N_USData.con
L_Data.ind(SF)
L_Data.req(FF)
L_Data.con(CF)
L_Data.req(SF)
L_Data.ind(FF)
L_Data.con(SF)
L_Data.ind(FC)
L_Data.req(CF)
L_Data.req(CF)
L_Data.req(FC)
L_Data.con(FC)
L_Data.ind(CF)
N_USData.ind
L_Data.ind(CF)
OSEK-COM
ISO11898
OSEK-COM
ISO11898
L_Data.con(FF)
L_Data.con(CF)
Message Level
(up to 4095 bytes)
CAN Frame Level
(8 byte incl. ext. addr))
CAN Frame Level
(8 byte incl. ext. addr))
Message Level
(up to 4095 bytes)
R
e
qu
e
s
t
R
e
s
po
ns
e
Application
Application
R
e
qu
e
s
t
R
e
s
po
ns
e
Figure 4: Service Primitives During a Request/Response Sequence in the Tester and the ECU 
The service specifications of ISO 11898 and OSEK-COM do not specify any implementation requirements but 
provide abstract service prototypes to support data exchange with the layers. The service primitive below is an 
extraction of ISO 11898 and shall be treated as an example for service primitives: 
Semantics of the L_Data.req primitive: 
L_Data.req (IDE 
IDENTIFIER 
DLC 
DATA) 
Where: 
IDE
= Identifies the IDENTIFIER
’s length 
IDENTIFIER
= Identifies the data and its priority (CAN Identifier) 
DLC
= Data Length Code 
DATA
= Data the user wants to transmit 
4.8 Network Layer Buffer Requirements. 
The USDT protocol allows for segmented messages up to a 
maximum of 4095 bytes. The amount of memory that each ECU reserves for network layer support shall be 
based on diagnostic and normal communication needs. A SPS programmable ECU may have different 
network layer buffer size requirements for normal operations (e.g., normal communications and diagnostics) 
than it does while it is being programmed. 
4.8.1 Buffer Requirements for Normal Operation and Diagnostics. 
The size of the network layer buffer 
used during normal vehicle operation (including diagnostics and excluding SPS programming) shall be 
optimized to minimize RAM requirements while still allowing for the reception and transmission of the largest 
normal communications or diagnostic message expected by that ECU. 
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