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

8.11.2.2 Request Message Data Parameter Definitions (Table 125). 
Table 125: Request Message Data Parameter Definition 
Definition 
parameterIdentifier 
The parameterIdentifier is a 2-byte number assigned to individual diagnostic signals or parameters. The 
parameterIdentifier (PID) number is used by the $2C service to build dynamic DPIDs or the $22 service to 
request specific diagnostic parameters
 
memoryAddress 
The parameter memoryAddress is used to select the starting address of ECU memory from which data is to be 
retrieved. A portion of the memoryAddress parameter (most significant bits or bytes) can be used as a 
memoryIdentifier. 
An example of the use of a memoryIdentifier would be a dual processor ECU with 16-bit addressing and 
memory address overlap (when a given address is valid for either processor but yields a different physical 
memory device). In this case, a 3-byte memoryAddress parameter can be specified and the most significant 
byte of the memoryAddress parameter could then be used to select which physical memory device the tester is 
attempting to retrieve data from. Any usage of a memoryIdentifier shall be documented in the appropriate CTS, 
SSTS or supplemental diagnostic specification referenced by the CTS or SSTS.
 
memorySize 
The parameter memorySize is used to select the number of consecutive memory addresses (in ascending 
order) to be read starting at memoryAddress (memorySize includes the starting location). MemorySize shall 
have a value between one and seven bytes. The maximum value comes from the maximum number of bytes 
allowed in a UUDT diagnostic response (of the $AA service).
 
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