Encoder voltages on a 7i77

Hi all,

I thougth I'd ask before I break my board.
I have encoders that output a differential signal of about 12V, is this a problem for the Mesa 7i77?

Thanks for your reply
Bram

No, the 7I77 inputs are 5V only, They receiver chips are 26LS32As which are protected against +-25V inputs
but when in differential mode the inputs are terminated with a 120 Ohm resistor, This resistor will be destroyed
by a 12V input voltage. One possibility is to add ~300 ohm resistors in series with all 12V encoder leads.
This will bring the common mode and differential voltages to acceptable levels

Ok, thanks,

I should have asked before buying the boards, but with resistors in series it should work. that's great!!

One question though, do you mean I have to put one 300 ohm resistor in series per differential signal
or 2, one on each side of the differential signal so 600 ohm in series?
The first option would put 3.4 volts over the 120 ohm resistor, but dissipates 0.244 watts in the 300 ohm resistor
The second option puts only 2 Volts over that 120 ohm resistor, is that enough?

Maybe I am completely wrong and things aren't as simple as R=U/I

2 resistors 1 in series with each leg
2V differential is plenty (input sensitivity is +-200 mv)