digital /analog switch/multiplexer for RS232 signals

rifo

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

over 8 years ago

0 ShreyasRao over 8 years ago

TI__Guru 58320 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 rifo over 8 years ago 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 ShreyasRao over 8 years ago in reply to rifo

TI__Guru 58320 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 rifo over 8 years ago 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 Ron Michallick over 8 years ago

TI__Guru*** 149776 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 Ron Michallick over 8 years ago in reply to Ron Michallick

TI__Guru*** 149776 points

Rifo,

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

0 rifo over 8 years ago 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

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digital /analog switch/multiplexer for RS232 signals