Making 3rd party Mesa daughter card: what are the voltage levels?

Like many of us, apparently, I ran out of IO's on my Mesa 7i96s as my CNC project got bigger. I'm in EU (Czech Republic) and I cannot find daughter card in nearby eshops, that is in stock and doesn't cost arm, leg and/or kidney. I'm cheeky enough to think that I can wire a simple IO card by myself. 

The question is: what are the voltage levels of the IOs on the IDC26 connector? I see someone connecting a parallel BOB directly, so is it 5V, or 3.3V since it is wired to the FPGA?

Thanks for info,
Martin

PS: If everything goes well with prototyping, I will make a custom PCB. Anyone else interested?

7I96 P1 voltage levels are basically 3.3V though
you can get 5V output swing using open drain
output mode. (all I/O have 4.7K pullups to 5V)
Daughtercard design need to consider that all
P1 I/O will be high at startup because of these pullups

All I/O pins are 5V tolerant.
Input thresholds are LVTTL so approximately 1.5V

Maximum input voltage is +7V
Minimum input voltage is -0.5V
Maximum source/sink current is 16 mA
(more negative than -0.5V without current limiting
will damage the input clamp diodes = 10 mA Max)

Also note that you can get power for your daughtercard
via P1

Thank you both of you. I've sifted through the manual for days, not finding this page. Shame on me.

I'm going to cobble together a simple 4-16 input card, because inputs are what I ran out. There will be optocoupler protection, maybe even input protection on the IDC26 side just like on the full fledged card. And some LED indication, possibly wrapped in some enclosure.

@PCW As I understand from other posts, you are a HW developer of the Mesa, is that correct? What is your (or the company's) stance on me building/sharing this and maybe selling as a 3rd party card? From my brief encounter with you and this wonderful community here, I wouldn't like to step outside of some boundaries, but rather give back in form of something, that isn't readily available via main channel. Thank you for answer in advance.

Have nice day,
Martin

I certainly don't have (or even could have) any objections to you making a compatible
daughtercard (or even main card since the hostmot2 firmware is all open source)

My only suggestion would be make sure that your daughtercard is general enough
that it works with other similar interfaces (Parallel, RIO, etc)

Did you mean to say you don't have ?

Or am I misunderstanding ?

Either way Pete your very very gracious with your time, even for those of us who experiment with your firmware on other hardware.