Mesa Smart Serial Interface Questions (expanding and/or encoder card options)

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29 Aug 2021 06:48 - 29 Aug 2021 06:56 #219072 by wrinkols
Working on a retrofit and I am running in to a dead end. I'll add some of the reasoning and background for the choices that got me here at the bottom of the post.

First:
Current setup is 7i95 + 7i83 + 7i73 but I'm running out of output. I'd really like to add another SSerial input card but I've already used the 2 available interfaces on the 7i95. I'm not that familiar with sserial, but a bunch of the Mesa explanations say you can just keep stacking up those cards. So my question on this is whether there is an option for adding another sserial interface to this card (or duplex one of the current interfaces?) preferably without adding a card to the 26pin connector.

Second:
Since I hit the above snag I thought about switching back to my original desired setup using a 7i94. Where I gave up on this option before was that I wanted either a dedicated encoder input card (differential encoders) or a card with step + direction and encoder inputs. I notice that the card can interface directly to encoders but it specifies absolute which makes me assume it won't work with mine (acu-rite linear glass scales ENC 125 using differential converter board).

Any thoughts on solutions for the above 2 issues? Thanks in advance

Background: Machine is a Shizuoka CNC knee mill that uses linear encoders and has analog -10/10 vdc servo drives. Right now all the original stuff works, but I don't anticipate them lasting forever. My thought was if I can make the retrofit modular I can (hopefully) just add new drives when/if the current one breaks (mix and match). Also, I really liked the idea of using eth cables for all the connections between cards. I wanted the 7i94 but could never figure out a good encoder solution without ending up with a 7i76 or something which seemed pointless when trying to base everything from the 7i94. Finally landed on the 7i95/7i83 setup figuring that way in the end I'll only have 1 card once all servos get converted to step/gen (+ mpg card). 
 
Last edit: 29 Aug 2021 06:56 by wrinkols. Reason: typo(s)

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29 Aug 2021 17:03 #219110 by PCW
You could add a 7I85S to a 7I94 to get 4 step/dir outputs and 4 encoder inputs
Or you could add a 7I74 to a 7I95 to increase the number of sserial channels

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29 Aug 2021 17:39 #219112 by wrinkols
That's what I was thinking the answer would be. Thanks for the swift reply. Out of curiosity, when the Mesa site says you can use up to 32 (I think?) do they mean you can connect 4X 7i94 to separate NICs on the computer? Also, it looks like all the daughter cards that support encoder/pwm are DB25 or similar. Is this a limitation of FPGA<->sserial speed/bandwidth?

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29 Aug 2021 18:33 #219118 by PCW
PWM would be possible on sserial as would encoders.
encoders use a lot of bits so it's not too practical to do multiple
encoders on a remote sserial card due to the current 96 bit
packet size limit (this has been expanded to 224 bits but no current
sserial remotes use more that 96 in and 96 out)

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12 Sep 2021 16:38 #220339 by wrinkols
I ended up going with 7i94, 7i83, 7i66-8, 7i85s.

For hal pins, the remote serial cards are straight forward since they all lay under hm2_7i94.0.7i83 ect. For accessing the 7i85 are these all through the gpio pins that are shown in hal? My assumption is "yes", but just wanted to verify. I'm not seeing any real indication with this card connected/disconnected that makes it obvious it's working. I guess the next step is to test it but just wanted to ask first.

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12 Sep 2021 17:13 #220342 by wrinkols
Sorry, found the whole part where I needed to write the bit file. After flashing the 7i94 it looks like we're good.

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