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

Note:
For the special condition of receiving a service $20 ReturntoNormalMode request on multiple 
subnets 
while in programming mode
, the MSSC shall perform the required reset (see section 8.5.1) after 
the first received service $20 request. It is the tester
’s responsibility to coordinate the service $20 requests 
on the multiple links so that the link, which requires a baudrate switch, receives the service $20 request 
first if the tester is connected to multiple subnets. 
2. For diagnostic services only supported on one subnet (e.g., service $AA), the MSSC sends the positive 
response on the subnet supporting the service while sending a negative response reject message (e.g., 
$7F $RequestServiceId $11 for service not supported) on the other subnet (a negative response is only 
sent if the request is physically addressed). 
4.4 Message Identification - Diagnostic CAN Identifiers (CAN Identifiers). 
Diagnostic CAN Identifiers (CAN 
Identifiers) are required in order to separate diagnostic messages from Normal Communication messages. The 
diagnostic CANId in a request message also determines the type of addressing used for that message, either 
physically addressed (targeted to only a single node) or functionally addressed (targeted to one or multiple 
nodes). 
4.4.1 Diagnostic CANId Definitions. 
Each GMLAN node shall support the following types of diagnostic CAN 
Identifiers unless otherwise stated in the descriptions below: 

Physical Request CAN Identifier (USDT): 
This CAN Identifier shall be used to transmit physically 
addressed single frame or multiple frame request messages to a single ECU utilizing the Network USDT 
protocol with normal addressing. This CAN Identifier shall also be used by the tester to send FlowControl 
frames to an ECU if the transmission of data from an ECU to the tester requires a multiple frame 
transmission. 
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