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

8.11.1 Service Description. 
The DefinePIDbyAddress service allows a tester to dynamically assign an ECU 
variable to a PID via the address of the variable. The resulting PID data can then be read using either the $22 
service or the $AA service. The service is intended to be used to retrieve RAM variables. Calibrations and 
unprotected areas of EEPROM/Flash memory should not be packed into a dynamic PID. This type of data is 
static in nature and can be obtained using service $23. 
The dynamic PID being defined is identified by parameterIdentifier (PID), memoryAddress (MA) and 
memorySize (MS). The size of parameterIdentifier is fixed at two bytes; the size of the memoryAddress 
parameter in the request message can be two, three, or four bytes in length depending on the ECU internal 
addressing scheme. The number of bytes that a tester shall use in the memoryAddress portion of the request 
message for a given ECU shall be documented in the appropriate CTS, SSTS, or supplemental diagnostic 
specification referenced by either of the preceding documents. The memorySize parameter in the request 
message can range from one to seven bytes. (Seven bytes is the maximum in order to allow the PID to be part 
of a DPID.) 
The DefinePIDbyAddress positive response message includes the parameterIdentifier (PID), specified in 
request message. 
A device may deny access to specific addresses in order to protect their operating system and other secure 
data. An ECU may also restrict the testers ability to read specific addresses based on the security status of the 
ECU. If any of the addresses (that fall in the range of the request message) have security restrictions then the 
request shall be rejected unless the tester had previously successfully accessed security. 
Note: 
Security access is only required if the ECU is locked based on the status of the MEC and/or the 
vulnerability flag see the SecurityAccess ($27) service for more information. 
The range of PIDs that can be dynamically defined by this service in a given ECU shall be documented in the 
appropriate CTS, SSTS, or supplemental diagnostic specification referenced by either of the preceding 
documents. 
Note:
If a tool requests a dynamic PID before this service is called to define the PID then the resulting 
response is undefined. 
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