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

8.11.8 Tester Implications. 
The tester needs to ensure that it transmits the correct number of bytes in the 
memoryAddress parameter or the message shall be rejected. 
If the tester attempts to request a dynamic PID (via the $22, $2C/$AA services) and the PID has not been 
previously defined via the $2D service, the results are undefined. 
If the tester packs a dynamic PID into a dynamic DPID, then attempts to redefine the dynamic PID (using the 
$2D service) without subsequently redefining the dynamic DPID, then the data transmitted when the DPID is 
requested is undefined. Anytime a tester has packed a dynamic PID into a dynamic DPID and wants to 
redefine the dynamic PID, then the tester should first remove the dynamic DPID from the DPID scheduler, 
redefine the dynamic PID, redefine the dynamic DPID and then put the DPID back into the periodic message 
scheduler (via the $AA service). 
This service should only be requested with physical addressing. 
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GMW3110 
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8.12 RequestDownload ($34) Service. 
This service is used in order to prepare a node to be programmed. 
8.12.1 Service Description. 
The service is used to indicate to the programming routines which encryption and 
compression techniques are utilized so that the programming routines can correctly decode the data received 
with subsequent TransferData ($36) services. This is a secured service. Nodes that support security access 
must be unlocked before a request for this service is accepted (see Mode $27 Request SecurityAccess). 
This service is also used by the test device to request a Node to transfer program operation from the 
application software to the boot software (for nodes that support a boot) so that the node can be programmed. 
ECUs that utilize the SPS system to program operational software are required to have boot software. See 
programming chapter within this specification. ECUs that have their software in ROM and utilize the SPS 
system to program calibrations are not required to support a boot. 
The DisableNormalCommunication ($28) and ProgrammingMode ($A5) services must be active prior to the 
mode $34 request. However, high speed programming (enabled with service $A5 on the Single Wire CAN link) 
is not required to be active to perform programming. This means that even though the intent is to perform 
programming in high speed mode (for devices on the low speed link), it will be possible to program these 
nodes in normal speed if circumstances dictate the need. 
Only a single $34 service request is required to initiate a download sequence of multiple software or calibration 
modules to the node. However, it is also possible to send a $34 service request each time a download of a 
single software or calibration module starts (clear separation of all downloaded modules).