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MSCAN SRR bit question

Question asked by gator on Sep 7, 2016
Latest reply on Sep 8, 2016 by Radek Sestak

According to the MSCAN datasheet, the SRR bit must be set to recessive when using an extended 29 bit identifier. However, I ran some tests with two interconnected MSCAN equipped devices using extended 29 bit identifiers and was able to send a message from one MSCAN device to another using 29 bit identifiers without the SRR bit being set. How is this possible if the SRR bit must be set recessive when using 29 bit identifiers?

 

The reason why I performed this test is because I noticed that a vehicle I was trying to request a VIN from was responding with the VIN in a message (with 29 bit identifier) that did not have the SRR bit set recessive - the SRR bit was set dominant. Since my MSCAN filter was set up to pass messages with the SRR bit set recessive, a filter hit was not generated and the MSCAN was not able to receive the VIN response.

 

Any ideas as to what is going on here?

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