Mesa 7i76 - setting nvencmode0 to 4 - how?

I am experimenting with linear glass scales. They are 5v TTL models with A+ B+. My 6i25/7i76 plug-n-go kit is running in mode 2 so I have the pins 16/17 connected up to A+ B+. The counts are coming through but the resolution is off. The scales are 5mu but the counts being shown are resolving to 0.02mm. I think the encoder is not counting correctly. That single count for 0.02mm should be 4 counts each at 0.005mm for the same distance covered.

I followed the discussion and process on this thread
forum.linuxcnc.org/27-driver-boards/3045...first-steps?start=20
but I am not getting the nvencmode0 value to change even though the set serial command says it is sucessful.

According to the linuxcnc 2.8 docs the setserial command says it is redundant unless flashing firmware and a setp in hal will work. It doesn't as the pin hm2_5i25.0.7i76.0.0.nvencmode0 is marked as RO.

Is there a utility or approach I am missing?
Is this not doable?
Do I need to upgrade firmware on the card?

Thanks for any assistance/advice the community is able to supply.

Thanks,
James.

James, Pins 16-17 are only good for MPG's so won't work with your scales. You'd need to add a Mesa 7i85 on the other 5i25 25 pin connector. You only have one encoder on your 7i76 for the Spindle.

The other thread was talking about a 7i77 which does have encoders (6 I think)

The encmode should not be Read Only, I'll take a look at it

Default is 1X quadrature mode which is appropriate for MPGs
since it will jog 1 increment per click

Note that the MPG inputs are only good to a couple KHz

PCW - thank you.

Appreciate the MPG encoder is “slow”. This is being done for testing purposes to prove out i can utilise this scale. Initial work has been mapping the ball screw. I’m now getting into some other checks in how I might use the scale. Movements are pretty slow, 100 to 150mm/min so hopefully within capacity of the MPG.

Ultimate game plan is to get an encoder daughter board like Rod mentioned.

Cheers,
J.

Rod - out of interest was there any particular reason you mention the 7i85 versus say the 7i89? Other than one is 20USD cheaper.

Cheers,
J.

Joco wrote:

Rod - out of interest was there any particular reason you mention the 7i85 versus say the 7i89? Other than one is 20USD cheaper.

Cheers,
J.

Oops, I better reprogram my grey matter! I just think 7i84 and 7i85. I just went through an email thread from PCW and we were just talking about the 7i84 and 7i85 but also wanted RS485 and smart serial... One is smart serial and the other plugs in.

With the 7i76e with lots of inputs, you might be able to experiment with the encoder component which is also slow....

With the 7i76e with lots of inputs, you might be able to experiment with the encoder component which is also slow....

Not sure what you mean by "slow".
I'm using 5um glass scales with a 7i76e on my mill and that works just fine. But my axis only go about 25mm per second so I'm not sure where the limit is there.
PCW would certainly be able to provide that information.

[edit]
I'm sorry I made a total mess of this. Somehow it changed the subject on me.

Aciera wrote:

With the 7i76e with lots of inputs, you might be able to experiment with the encoder component which is also slow....

Not sure what you mean by "slow".
I'm using 5um glass scales with a 7i76e on my mill and that works just fine. But my axis only go about 25mm per second so I'm not sure where the limit is there.
PCW would certainly be able to provide that information.

Hi. In this context "slow" is relative. Compared to the h/w encoder it is slow. But it might well be fast enough to do the job. your 25mm/sec is actually about my rapids speed.

While I have a 6i25/7i76 combo at the moment I plan to move to a 7i76e. I would be VERY interested in how you are doing things. Do you have scales on three axis or just the X/Y? If all 3, how are you doing that?

If there was a way to get 3 MPG encoders running (given I have an abundance of spare inputs) that would be AWESOME.

Cheers,
James.

James,

Rereading my post I just realized I forgot to mention the fact that I use a 7i85 connected to the 7i76e. Should have had my coffee first I guess. So really I totally failed to understand that you want to use the MPG inputs for the glass scales. That of course is something totally different to using the dedicated encoder inputs of the 7i85.
Now I understand why Rod said it's would be slow.

[edit]
Aw, jeez. It changed the title of the post as well! Can somebody change that back please?

I don't think there is much point going from a 7i76 to a 7i76e.
What I was thinking of was to use the encoder component on some spare input pins...
linuxcnc.org/docs/2.8/html/man/man9/encoder.9.html

I think the OP needs to edit the first post title and also add another post with the same title to change the topic. the forum has a mind of its own here...