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Discussion Groups | 68HC12 | CAN receivers
Join our technical discussions about Freescale Microcontrollers: M68HC12. (Freescale Semiconductor is a Subsidiary of Motorola).
CAN receivers - Trevor Wigle - Nov 6 13:03:00 2002
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Hello all, I am currently using a 912DG128 with two CAN peripherals. I only use one but I am wondering if there would be any problem with connecting just the Rx pin of the second CAN module to the Rx pin of the module I am using. The reason I would want this configuration is then I would have twice the receive identifier masks available. I am concerned with how the peripheral will react when it sends an acknowledge on the Tx pin (which is connected to nothing) and doesn't receive the acknowledge on the Rx pin. This could happen during system startup when there are no other nodes powered up. That is the only hang-up I can see but if there is something I am missing please let me know. TIA, Trevor Engine Control and Monitoring (ECM) 586 Weddell Drive, Suite 2 Sunnyvale, CA 94089-2134 USA (408) 734-0522 fax (408) 734-3432 |
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RE: CAN receivers - Kellogg Dave - Nov 6 14:03:00 2002
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I have not actually done what you are suggesting (parallel receivers), but I have thought it through and I believe that it is feasible. I think that I have also (somewhere) seen an app note by ??? showing this done. About the ACK bit: First, listeners are the ones that drive this bit. Secondly, for this special bit, I thought that listeners did not monitor the bus to see that the bus actually went dominant. 607-656-2597 -----Original Message----- From: Trevor Wigle [mailto:] Sent: Wednesday, November 06, 2002 1:04 PM To: 68HC12 Subject: [68HC12] CAN receivers Hello all, I am currently using a 912DG128 with two CAN peripherals. I only use one but I am wondering if there would be any problem with connecting just the Rx pin of the second CAN module to the Rx pin of the module I am using. The reason I would want this configuration is then I would have twice the receive identifier masks available. I am concerned with how the peripheral will react when it sends an acknowledge on the Tx pin (which is connected to nothing) and doesn't receive the acknowledge on the Rx pin. This could happen during system startup when there are no other nodes powered up. That is the only hang-up I can see but if there is something I am missing please let me know. TIA, Trevor Engine Control and Monitoring (ECM) 586 Weddell Drive, Suite 2 Sunnyvale, CA 94089-2134 USA (408) 734-0522 fax (408) 734-3432 -------------------------------------------------------- To unsubscribe from this group, send an email to: To learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu |
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Re: CAN receivers - Steve Letkeman - Nov 6 14:34:00 2002
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Hi Trevor, I think that what you're trying to do would work because the Rx port will see the Ack bit from the other connected port. But, you might consider that if the receiver receives an error, it might try and send an error frame and without the transmitter connected it might then go bus off. (eventually) I haven't tried this but it seems like it might happen. As a possible solution, consider adding a reversed diode to each of the TX pins so that if either of them goes low, the transceiver will transmit. (Add a pullup on the transceiver) Both of the RX pins could be tied together. This would bus the two ports together without having a second tranceiver needed. Again, I haven't tried this but it should work. Steve Zanthic Technologies Inc. is located at www.zanthic.com Your Controller Area Networking Experts! Embedded micro-controllers and CAN interface devices sold here ----- Original Message ----- From: Trevor Wigle To: 68HC12 Sent: Wednesday, November 06, 2002 11:03 AM Subject: [68HC12] CAN receivers Hello all, I am currently using a 912DG128 with two CAN peripherals. I only use one but I am wondering if there would be any problem with connecting just the Rx pin of the second CAN module to the Rx pin of the module I am using. The reason I would want this configuration is then I would have twice the receive identifier masks available. I am concerned with how the peripheral will react when it sends an acknowledge on the Tx pin (which is connected to nothing) and doesn't receive the acknowledge on the Rx pin. This could happen during system startup when there are no other nodes powered up. That is the only hang-up I can see but if there is something I am missing please let me know. TIA, Trevor Engine Control and Monitoring (ECM) 586 Weddell Drive, Suite 2 Sunnyvale, CA 94089-2134 USA (408) 734-0522 fax (408) 734-3432 -------------------------------------------------------- To unsubscribe from this group, send an email to: To learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu [Non-text portions of this message have been removed] |
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