FPGA and RS422

Possible, yes. Practical, maybe not. Most FPGAs have differential IP modes, so could accept RS422 IPs, with the caveat, WITHIN their common mode range. For true RS422/485 devices, that is around -7V..+12V, which allows ground movement between ends of the cable. FPGA pin common mode is much less than this, but you could extend it with a resistor pad (which also attenuates the wanted signal ) Then there is ESD protection. Most separate RS422/485/CAN transcievers have higher tolerance to ESD, than FPGA.

RS422 output needs sufficent drive current, and balanced drive, but that is within the capability of FPGA. For short-haul, and within-the-box signaling, this could be do-able, but perhaps not for connection to 100m cables in a factory...

-jg

To further that thought, if you use a transformer you can remove the common mode votages, and bias them yourself on the isolated side of the transformer. This is documented in Crystal semiconductor products since digital audio uses RS 422 for transmission. See CS8415 data sheets and app notes. A couple of transient voltage suppressors as well and you're in business.

Thanks for the information

I think I will go for the interface chip it looks like the most simple solution.

Cheers Rune

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common

FPGA