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

9.2 Requirements for All ECUs to Support Programming. 
The following applies to all ECUs on the link (not 
limited to the node actively being programmed): 

The ProgrammingMode ($A5) service shall be used by the ECU to recognize the start of a programming 
event. 
1. During a programming event, ECUs shall default their physical input/output (I/O) pins (wherever possible 
and without risk of damage to the ECU/vehicle and without risk of safety hazards) to a predefined state 
which minimizes current draw. 
2. ECUs shall ensure that they can handle 100% bus utilization at any allowed programming baud rate 
without dropping frames during the programming event. An ECU may need to modify its hardware 
acceptance filtering to only receive the AllNodes CANId (non-programmable ECU), or the AllNodes CANId 
and either the diagnostic point-to-point CANId or SPS_PrimeReq CANId (for programmable ECUs) in 
order to meet this requirement. 

The DisableNormalCommunication ($28) service shall be used by the ECU to recognize the disabling of 
normal communication and to ensure that an ECU does not set DTCs while another ECU is being 
programmed. This includes not only disabling the transmission of normal communication messages, 
but 
also disabling the processing of any received normal communication messages.
Note:
There may be some vehicle link configurations where a mode $10 request must be sent prior to the 
Mode $28 to ensure no DTCs are set when normal mode is disabled. 

The receipt of a ReturnToNormalMode ($20) request shall be used by the ECU to conclude an active 
programming event. At the conclusion of a programming event, each ECU shall perform a software reset, 
and all fully programmed ECUs shall resume normal communications (including re-enabling DTCs). For 
special issues regarding resets for MSSC devices, see paragraph 4.3.4. 

The TesterPresent ($3E) service shall be used by the ECU to recognize that the active programming event 
is still in process. 

The ReadDataByIdentifier ($1A) service and the DataIdentifier $B0 (diagnosticAddress) shall be supported 
by the ECU in order to provide the tester its diagnostic address. The diagnostic address information in 
conjunction with the ECU CAN Identifiers is used by the tester to recognize the correct response(s) of the 
ECU(s) connected to the GMLAN subnets during the Pre-Utility File Process. MSSC ECUs shall support 
this functionality on each GM LAN subnet they are connected to. SPS_TYPE_C ECUs are not required to 
report the diagnostic address when executing out of the boot software as this information can be obtained 
from the SPS_PrimeRsp CANId. 
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