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switching device CAN - RS232

Ryuji
Guru 20090 points

Other Parts Discussed in Thread: SN65HVD1050, SN65HVDA540-Q1, CD4055B, CD4066B-Q1

Hello,

Are there any switching device or Application for switching CAN - RS232?
Please see the attached picture.
I serarched digital logic device, mux device in website, but I can't find the device which we can use it.

Best Regards,
Ryuji Asaka

  • 0
    TI__Guru** 103215 points

    Hello Ryuji,

    There is a TI reference design for a multi protocol RS-485/RS-232 transceiver system which can be found here:  

    This design is fairly simple, basically the FORCEOFF pins on the RS-232 transceivers are tied together and used to switch the device into RS-485 mode and likewise, the DE and RE pins on the RS-485 transceivers are toggled to switch the device back and forth between modes. For this design the modes are toggled with a simple jumper as seen on the schematic:

     

    It should be relatively simple to extend this basic idea to a RS-232/CAN switching device. For example, using a CAN device with the "Silent Mode" feature, the CAN transceiver could be placed into listen-only mode while the RS-232 communication is taking place on the bus line. The above circuit could be modified to allow mode control via the CPU rather than by jumper. The SN65HVD1050 is an example of a CAN device with this Silent Mode feature. 

    On thing to note about this strategy is that the receiver for the CAN device would be enabled during RS-232 communication. This may or not be an issue depending on your application. If your design uses two separate TX and RX lines in the TTL section as shown in your diagram, then the CAN receive line could simply be ignored during RS-232 communication. If they operate on the same TX and RX lines, then there could be an issue of interference between the RX lines of two devices. More details about the application could help to determine if this is a viable option for you. 

    Best Regards,

    Casey McCrea

  • 0
    TI__Guru**** 169476 points
    Ryuji,

    Our logic apps engineer suggested the CD405xB series of mux ,which has dual supply up to 18V .
  • 0 in reply to Casey McCrea
    Guru 20090 points
    Hello McCrea san,

    Thank you for your support.
    I will propose this reference design.

    Can we porpose the SN65HVDA540-Q1 for CAN tranceiver?
    The SN65HVD1050 has Silent Mode , however the SN65HVDA540-Q1 has Standby mode.
    Thus, we can disable the receiver of CAN device when we use the SN65HVDA540-Q1.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ron Michallick
    Guru 20090 points
    Hello Michallick san,

    Thank you for the information.
    Since the voltage level is +/-13V , we can't use these device.

    If the 18V is acceptable, can we use CD4055B-Q1 ?
    The customer would like to use Automotive qualified device.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Guru** 103215 points

    Hello Ryuji,

    The standby mode of the SN65HVDA540-Q1 may cause issues vs. silent mode because in standby mode, the bus lines are weakly biased to ground. Silent mode will put the bus outputs in a high impedance state which will ensure that the CAN device doesn't interfere with operation of the RS-232 device. 

    As for the CD4055B-Q1, Ron may be able to give you more insight.

    Best Regards,

    Casey 

  • 0 in reply to Ryuji
    TI__Guru**** 169476 points

    Ryuji san,

    CD4055B is not Q1. It is a CMOS BCD-to-7-Segment LCD Decoder/Driver with Display-Frequency Output. Was there a different device in mind?

    I believe the logic device recommendation did not consider a negative -13V signal.

  • 0 in reply to Casey McCrea
    Guru 20090 points
    Hello Casey san,

    Thank you for the reply. I understood that we can't use the standby mode for this multiprotcol design.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ron Michallick
    Guru 20090 points
    Hello Ron san,

    Sorry. CD4055B is a mistake of CD4066B-Q1.
    However, I understood that we can't use these devices for negative -13V signal.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Guru**** 169476 points
    Casey,

    I see that silent mode will make the CAN device basically invisible when used in RS232 mode.

    The RS232 driver can go high impedance. The RS232 receiver has a 5k resistance to ground.
    If this 5k to ground was connected to one of the CAN lines, would that affect CAN signal quality?
  • 0 in reply to Ron Michallick
    TI__Guru** 103215 points

    Ron,

    I suspected this would be ok if one of the CAN lines was pulled 5k ohms to GND but I did some testing in the lab to confirm. As expected, the recessive level will be pulled down towards ground, but the driver is still able to establish a valid dominant level on the bus with no problems. I tested both situations, CANH pulled to GND and CANL pulled to ground, and found no issues with sending/receiving data. I tested data rates from 100kbps to 1Mbps with the SN65HVD1050.

     Best Regards,

    Casey