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digital /analog switch/multiplexer for RS232 signals

rifo
Expert 1105 points
Other Parts Discussed in Thread: MAX232

Hello,


is there an IC in TI portfolio that I can use to digitially control for switching/multiplexing on / off RS232 signals?

In my search, I wasn't able to find one due to negative voltage level requirements for RS232

I have an application where multiple controller modules are connected serially. Each controller acts as a uart forwarder and thus the system can scale up / down without any problems

I am looking for a fail safe mechanism for the case where a controller module fails to function properly due to a problem (MAX232 chip dead) and kills the communication with the rest of the healthy, functioning modules connected to it.

I thought that I can route a bypass track connected to a switch for the RS232 signals and then in case a problem occurs,  the switch can be turned on automatically  to bypass the problematic controller module.


thanks a lot

rifo

  • 0
    TI__Guru 60020 points
    Hi Rifo ,

    The negative swing for the switch is the harder part . do you have the requirements in place ?
    We have CD4051/ 52/53B switches which are negative voltage capable , I am unsure if it can support RS232 level signals levels though .
  • 0 in reply to ShreyasRao
    Expert 1105 points

    Hello Shreyas,

    Thanks for your reply. I am using a Max232 from TI as the RS232 level converter. Which requirements are needed to find an appropriate IC ? If you can tell me then I can write it.


    thanks

    rifo

  • 0 in reply to rifo
    TI__Guru 60020 points
    Hello Rifo ,

    requirements being the voltage levels being used . I have also tagged my colleague to help in narrowing down and helping on RS232 signaling .
  • 0 in reply to ShreyasRao
    Expert 1105 points

    Hello Shreyas,

    I have checked the datasheet of Max232R and it says that ttl/cmos voltage levels will be converted to IA/EIA-232-F levels for RS232.

    thanks a lot

    rifo

  • 0
    TI__Guru**** 158516 points

    Rifo,

    Because the most common "CM" failure will be it turned off or unplugged, I suggest using a physical relay. Relay normally closed contacts work even when there is no power.

    A DPDT relay can bypass the RS232 through the "CM" and remove the 5k load of the bypassed receiver.

    The driver outputs are still connected but won't be a problem unless the driver output is shorted.

    Here is a drawing, (ignore pin numbers)

  • 0 in reply to Ron Michallick
    TI__Guru**** 158516 points

    Rifo,

    with a 4 pole double throw relay(s), full bypass can be achieved.

  • 0 in reply to Ron Michallick
    Expert 1105 points
    Hello Ron,

    thanks a lot for your answer. I have checked digikey for solid state relays and there are many alternatives. I'll implement your method of bypassing to my system.

    thanks a lot
    rifo