mesa 7i76E - new pinout?

Hello,

after fiddling around a 7i80HD I'd like to go for a 7i76E - from the numbers of pins it should be fine, but the original pinout is too much wastage of pins. My stepper drivers have differential interface, so I don't need 5V and GND on the stepper channels. So I painted a new pinout.
Is it possible to achieve such a pinout with the 7i76E?




... and is there anybody willing to help me create a new bit-file?

I tried to download the xilinx ise, but I'm from outside of us and xilinx wants to verify my phone too

OK, thanks for the hint. Then I'll try another one.

Ok, when the support-lines are hardwired, I'll only have changes for the expansion slots:


both have the same pinout, so that I can use the same daughterboard layout for both.

The MPG-channels will then be attached to field-I/O - do I need special treatment for those channels?

You cannot use bare FPGA pins for differential inputs (except LVDS which will not work with encoders)

Differential signals from encoders are used as a way of rejecting common mode noise, Standard RS-422 receivers
can detect as little as 200 mV of differential signal in as much as +-7V of common mode noise. The FPGA inputs in differential mode have a much smaller common mode range. Also Note the 7V of common more noise will destroy the FPGA chip in microseconds. It might be conceivable to use LVDS inputs with balanced resistive divider for each encoder input but not sure whether that's worth the effort.

Also in general its not suggested to drive step drives directly with the FPGA outputs. This can work if the FPGA is driving step drives with optocouplers with a common 5V (common Anode) connection and the FPGA is sinking current,
but is unlikely to work well for differential outputs since the outputs will not source current above 3.3V


If you want additional step/dir outputs and differential encoder inputs I would suggest adding 1 or 2 7I85S daughtercards

Thank you very much for your attention!
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PCW wrote:

You cannot use bare FPGA pins for differential inputs (except LVDS which will not work with encoders)

Differential signals from encoders are used as a way of rejecting common mode noise, Standard RS-422 receivers
can detect as little as 200 mV of differential signal in as much as +-7V of common mode noise.

Ok, that sounds reasonable.
Does it mean, that the step/dir pins from 7i76E have LVDS drivers?

My stepper drivers are Leadshine 3DM683 and LiChuan LCDA86H.
www.leadshine.com/UploadFile/Down/3DM683m.pdf
components-electronic-electrical.europag...el%20example)~3.html
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PCW wrote:

If you want additional step/dir outputs and differential encoder inputs I would suggest adding 1 or 2 7I85S daughtercards

I see - but that combination seems to expensive. The competitor is beamicon2 with cncpod2 for about 300 bucks (I'll have to create a daughterboard on my own). I'd prefer linuxcnc, but currently I don't see how I could solve my needs.

May be 7i80HD was a better choice. The cncpod2 is something like 7i92 - so I already went for a bigger mesa card.
Are AM26C31/AM26LS32 from TI the right choice for protecting FPGA pins and support differential interfaces?

Can you help me create a bitfile for the mesacard of choice?

26LS32s are commonly used receivers for differential encoder signals and work well

26LS31s are not commonly used for differential drivers for step motor drives
because they dont have more than about a 3V output swing under load

As far as expense goes, I think you are somewhat comparing apples to oranges
The Benezan products you list do not AFAICT have multiple high speed encoder inputs

PCW wrote:

As far as expense goes, I think you are somewhat comparing apples to oranges

You're right! With Benezan I have only one choice, so with linuxcnc I already thought about oranges instead of apples and was willing to pay more (benezan price includes software license).

But anyway - may be I was wrong respect to the encoders. I wanted to have an upgrade path for small servos, but after a quick research it looks like leadshine offers the same interface for small servos as for CL steppers. So may be, I don't need the encoder channels.
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andypugh wrote:

... (and ethernet?)

Yes, ethernet is fixed for the following reason:
I have about 3-4m from Stepper-Drivers to Screen and if I place the PC next to the Stepper drivers, I need long cables for screen, keyboard, mouse, whatever ...
If I place the PC next to Screen, I only need an Ethernet-cable from PC to Controller, which will be next to the Stepper drivers.

Regarding my requirements, I'll start with 5 CL steppers, a spindle channel, 6 endstops, 4 relais and 3 MPG channels and several IOs for pushbuttons ...
My upgrade path is 2 additional stepper channels and 3 endstops.

So if I can drive 7 steppers at reasonable price, I would prefer that instead of switching stepper channel.
And yes, if there's a good reason, I'll keep on thinking about oranges and don't care for apples.