Interpreters Document

Typical Interpreter Line: (all Action and Goto fields are hex numbers) 
Step 
Op-Code 
Action Fields
Goto Fields 
11 
OP 
B4 03 10 00 
65 12
 FD
2A
FF
4A 00 00 00 00 
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Class 2 Response Processing 
 
Supported By:
Class 2 Interpreter 1 
 
Description: 
 
The Response Processing defines how the tool deciphers the response(s) returned from a control module 
after a successful request has been transmitted to the control module **. 
The response buffer fields, filled when a controller responds to a message, are identified as follows: 
Byte 1
- Priority and Message Type 
Byte 2
- Target Address
(typically targeted to the tester device) 
Byte 3
- Source Address (typically sent from a control module)
Byte 4
- Message ID
(typically a positive/negative response ID) 
Byte 5
- Misc. Response Data (N = 4096 bytes max.) 
Byte N+5 - High Byte of Block Transfer Message Checksum 
Byte N+6 - Low Byte of Block Transfer Message Checksum 
** 
Note
:
-
There are some Class 2 Op-Codes that send out a request and do not look for a response (i.e. Ignore 
Response). 
-
There are some Class 2 Op-
Codes that send out a request and don‟t care if there are no responses 
(i.e. Ignore Error). 
-
There are some Class 2 Op-
Codes that do not support the “no comm.” („FD‟) processing. 
These special cases are defined within the individual Class 2 Op-Codes. 
Pseudo Code: 
“Ignore Response” Processing 
If the op-
code specifies a response processing type of “Ignore Response” 
No response messages will be processed (read) from the vehicle communication link. 
Response 
processing will return immediately with “Success” after the request has been transmitted 
Endif 
“Ignore Error” Processing 
If the op-
code specifies a response processing type of “Ignore Error” 
The response data (one or more messages) WILL be processed (read) from the vehicle communication
link (based on “FE Response Processing” or “Individual Device Response Processing”). 
Regardless of whether the response is a positive, negative, or no response is received, response 
processing will return with “Success” 
Endif 
“FE” (all devices) Response Processing 
If the request message is targeted to “all” (FE) devices 
Process the response from the controller(s) on the vehicle communication link 
(only for controllers that respond to the “FE” request) 
If a negative (
7F) response is processed from one of the “responding” controllers 
Return immediately with “failed” (negative response) and the data from the negative response 
Endif 
Wait for 2 seconds of no responses being processed (idle vehicle communication link) 
If after 2 seconds there have been NO responses processed (zero in total) 
Return with a “no communication” response 
Else 
Return with “Success” and the data from the last response processed 
Endif 
Endif 
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“Individual Device” Response Processing 
(continued)
If the request message is targeted to a “specific“ device (ex. $10, $11, $18, $28, $40, …) 
Process the response from the controller on the vehicle communication link 
If a positive response was received (Response Message ID = Mode Number + $40) 
Return with “Success” and the positive response data 
Endif 
If a negative response was received (Response Message ID = 0x7F) 
If the last byte of the response is a $23 (Routine Not Complete) 
Wait up to one more second for an additional (positive/negative) response 
If no more responses are received (in the 1 second) 
Return with “failed” (negative response) and the data from the (0x7F . . . 0x23) response 
Endif 
Endif 
If the Response Message “target address” does not equal the Request Message “source address” 
Keep attempting to process responses from the controller 
If no more responses are received (in the remaining amount of time) 
Return with “failed” (negative response) and the data from the mis-matched target/source 
response
Endif 
Endif 
Endif 
If “no response” was ever received from the individual device 
Return with a “No Communication” response
Endif 
Special Mode $36 Response Processing 
If a positive response was received (Response Message ID = $76) 
If “response code” data byte is a $78 or a $6F (Response Data Byte #2 – “action not yet complete”) 
Keep attempting to process responses from the controller until a “true” positive or negative is
received 
Endif 
Endif 
Endif 
 
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
1993-2011 General Motors Company, GM Customer Care & Aftersales. All Rights Reserved.
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