CAN communication

Prit Gala

Other Parts Discussed in Thread: CONTROLSUITE

I'm recently working with the CAN communication protocol. I have a little doubt regarding the . Global Acceptance Mask Register (CANGAM) Field Descriptions.

The datasheet of CAN comm mentions that when

a)AMI bit=1

"The IDE bit of the receive mailbox is a "don't care" and is overwritten by the IDE bit of the transmitted message. The filtering criterion must be satisfied in order to receive a message. The number of bits to be compared is a function of the value of the IDE bit of the transmitted message."

b)AMI bit = 0

The identifier extension bit stored in the mailbox determines which messages shall be received. The IDE bit of the receive mailbox determines the number of bits to be compared. Filtering is not applicable. The MSGIDs must match bit-for-bit in order to receive a message.

So does it mean that when AMI bit =1 we dont need MSGID to recognize the incoming message or does it mean that the extended identifier in the CAN message is not required?

If it means something else please help me to understand the same.

Thank you.

over 9 years ago

0 Christopher Chiarella over 9 years ago

TI__Mastermind 30255 points

Hello,

If you look at the description for the IDE field, you make find it clearer to understand. When AMI is set, the message incoming sets the IDE bit for you but you must have appropriate acceptance filtering setup to be able to receive the message.

Best Regards

Chris

0 Prit Gala over 9 years ago in reply to Christopher Chiarella

Prodigy 35 points

I recently came across the IFxMSK bit and UMask bit in the IFxMCTL register. Can u please help in knowing what are these two registers and will any changes in these registers help in receiving the CAN message without a message ID?

0 Christopher Chiarella over 9 years ago in reply to Prit Gala

TI__Mastermind 30255 points

The registers you are referring to are only for the DCAN IP. Due to your tag on the post, I assume you are using a F28335 device which has the eCAN IP.

Here are some resources that can help detail eCAN functionality for F2833x.

F2833x eCAN TRM: www.ti.com/.../sprueu1.pdf (There is an acceptance filter section that discusses local and global filtering)
eCAN App Note: www.ti.com/.../spra876a.pdf

Additionally, the controlSUITE package has examples.

Best Regards
Chris

0 Prit Gala over 9 years ago in reply to Christopher Chiarella

Prodigy 35 points

That was helpful Chris. Thanks for mentioning the difference. Yes, I'm definitely using 28335 and it has eCAN.

Finally I have one last doubt. I have a battery that is is transmitting 20 strings. I'm want to receive those strings on 28335 using eCAN. However i don't the message ID of the incoming strings. Is there any other method by which I can obtain those strings using eCAN of 28335? Is there any bit that needs to be masked or enabled so that i can receive the strings without the message ID?

Thanks

0 Gautam Iyer over 9 years ago in reply to Prit Gala

Guru 192875 points

You can mask all the MsgID bits to receive to a particular Mailbox. Simply Set AME bit and configure ECanaLAMRegs.LAM2.all = 0xFFFFFFFF;

for mailbox 2.

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CAN communication