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

Definition 
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). The contents of the 
range of addresses defined by memoryAddress and memorySize are provided in the positive response 
message. memorySize shall have a value between 1 and 4092 bytes if a 2-byte memoryAddress parameter is 
used (4091 if 3-byte addressing is used and 4090 if 4-byte addressing is used). The maximum value comes 
from the maximum number of bytes allowed by the USDT protocol, less the bytes for the response service 
Identifier and the address information from the request message which is included in the response. An ECU 
may choose to limit the maximum value of memorySize based on ECU resources (e.g., the size of the Network 
Layer Buffer). If an ECU limits the maximum value of the memorySize parameter, then the maximum allowed 
value shall be documented in the appropriate CTS or SSTS.