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

GM WORLDWIDE ENGINEERING STANDARDS 
GMW3110 
© Copyright 2010 General Motors All Rights Reserved 
February 2010 
Page 157 of 336 
Table 133: Request Data Parameter Definition 
Definition 
dataFormatIdentifier
This data parameter is a one byte value with each nibble encoded separately. The high nibble specifies the 
compressionMethod
, and the low nibble specifies the 
encryptingMethod
. The value 
“$00” specifies that 
neither compressionMethod nor encryptingMethod is used. If no compression or encryption techniques are 
used, the unCompressedMemorySize bytes are transmitted as part of the request but their values may be 
ignored by the ECU. 
UnCompressedMemorySize
This data parameter can vary from two to four bytes based on the needs of the ECU (e.g., length of modules to 
be downloaded). The same number of bytes shall always be used for this parameter in all RequestDownload 
service requests for a given ECU. A programming tool determines the number of bytes to transmit on the bus 
based on data contained in the utility file (reference the programming chapter within this specification and also 
the Interpreter Specification listed in the Normative References section of this specification for more details). If 
compression or encryption techniques are used during programming, the data contained in the 
unCompressedMemorySize parameter shall be used by the Node to compare against the uncompressed size 
of the total data transferred with subsequent TransferData ($36) service requests. The total data transferred 
can either be a large block of data that contains all software and calibration modules (single service $34 
request), or a block of data that contains a single software or calibration module (multiple service $34 requests, 
one for each module). 
8.12.3 Positive Response Message Definition (Table 134).