RS422 Interruption: How to force a droupout in RS422 line.

Keith Barkley

Part Number: ISO1176
Other Parts Discussed in Thread: THVD1410, THVD1452, RS485-FL-DPLX-EVM

We have a troubleshooting issue where we want to force a dropout in an RS422 line.

I was thinking that I would use a pair of these and convert the signal from 422 to digital and digital to 422 with an enable along the way.

Isolation is not strictly required, but this was the first chip I found with an enable control.

over 5 years ago

0 Dan Kisling over 5 years ago

TI__Expert 6195 points

Hi Keith,

Could you explain to me what you mean by "force a dropout"?

Most RS485/RS422 transceivers have a driver enable pin and a receiver enable pin (typically denoted DE and /RE). A non isolated example is the THVD1410.

Best regards,

Dan

0 Keith Barkley over 5 years ago in reply to Dan Kisling

Guru 38560 points

Simply to switch the RS422 stream off for a given amount of time. If I was fast enough, I could use a toggle switch. 8^)

I will check out those devices in the morning.

0 Keith Barkley over 5 years ago in reply to Keith Barkley

Guru 38560 points

Actually the 1452 looks good, are their EVM's available?

0 Miguel Robertson over 5 years ago in reply to Keith Barkley

TI__Guru 62910 points

Hi Keith,

THVD1452 is compatible with this EVM:

Best regards,

Max

0 Keith Barkley over 5 years ago in reply to Dan Kisling

Guru 38560 points

It looks like the RS485-FL-DPLX-EVM will work perfectly for me. And digikey has them in stock! Any gotchas I should be aware of?

0 Miguel Robertson over 5 years ago in reply to Keith Barkley

TI__Guru 62910 points

Keith,

The only think I can think of that can be tricky with these boards is that there are 50-Ohm termination resistors on the digital inputs (D, DE, etc.). This is convenient when driving the board via a function generation through a 50-Ohm cable, but would likelt overload the output of a standard MCU/UART/etc. So, you may want to pull these off the board. Note that the termination is actually to the "earth ground" net of the board rather than the "DUT ground," so you could also just leave "earth ground" floating to accomplish the same thing. (That separate ground exists only to make it more convenient to test communication in the presence of ground shifts between nodes, and most people don't seem to use it.)

If you have any questions once you get the board just let us know, though. (It would probably be more visible if you created a new thread.)

Regards,
Max

0 Keith Barkley over 5 years ago in reply to Miguel Robertson

Guru 38560 points

Thanks! I think you have answered my questions

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RS422 Interruption: How to force a droupout in RS422 line.