Serial Doughter card 7i84 directly to FPGA card.

Hello, 
is there any easy solution to connect 7i84 serial daughter card directly to FPGA 5i25 card, without 7i74 - 8 channel RS-422 or some other DB25 daugther cards which has serial interface port? Maybe over a TTL to RS-422 signal converter?
Thanks. 

Yes, a TTL <-> RS-422 interface is all that's needed.

Basically, a single chip is enough (a SP491 or similar)

Take a look at this thread:

forum.linuxcnc.org/27-driver-boards/4578...chip?start=20#none-1

Hello,

i made a TTL <-> RS-422 converter circuit with MAX 491 CPD chip, flashed the FPGA and its worked perfectly, all cards are recognised... until i enabled the little (400W) servo driver in the enclosure.
In the same time when enabled the drivre the communication is stopped with 7i84 which is on the coverter card. The other 7i84 card (on the 7i76) continued to work without problem (green LED blinks).
If i not enable the driver, the system works hours.
The converter card is connected with the same DB25 cable like on the 7i76 (1,8m long). Beside chip is a 100nF 100uF capacitors on the power line.
Has anybody experience with this? The interferece/noise from the servo driver can block the communication? How can i filter the tx/rx line like in the 7i76 card?
If i enabled a little frequency regaultor, the system works without any problem. 

 
 
 

I would suspect a signal integrity issue, probably in the DB25
cable to your adapter (where you have TTL level signals)

Are you using all GND pins and all 5V pins on the DB25 cable to your adapter?

(I would use DB25 cable 5V to run your adapter to avoid ground loops)