Using 7i78 step generators with 7i76e

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27 Sep 2019 00:55 - 27 Sep 2019 00:57 #146308 by 5r100w
Hello all,

I am new to linuxcnc but have done a lot of reading on here and first would like to thank all the contributors as I have been able to set up a 7i76e with 5 step generators and have all axes on my machine homing and behaving correctly after initial setup with pncconf.

Now I need one more step generator for an independent axis and I have purchased a single 7i78 card to connect to the 7i76e.

I have flashed 7i76e with the 7i76e_7i76x1_7i78x1D.bit file which I found in another users post.

It does not appear that pncconf supports 7i78 so I realize that I need to code this manually in the hal and ini files.

I have been unable to figure out how to do this. In the beginning of my HAL file I changed the number of step generators in the statement:

loadrt hm2_eth board_ip="10.10.10.10" config=" num_encoders=1 num_pwmgens=0 num_stepgens=9 sserial_port_0=00xxxx

I did this with the assumption that because of the bitfile I have loaded, I can now manually add additional step generator/axis in HAL and INI file with HAL command like "setp hm2_7i76e.0.stepgen.xx.CC" where xx is additional step generators 05 thru 09 and CC are the setup commands for the axis but it does not work. I am reading the HOSTMOT2 manual but I can find little information about using the 7i78. I understand that this board just extends the P1/P2 connector of the 7i76e but I don't understand what I am doing wrong yet.

For reference, I already have 5 axis connected to the 7i76e, this is X1, X2, Y1, Y2, and Z1, all have home switches connected to digital inputs 0-4 and all are homing and moving well. All use servos with motion controllers which accept step/direction inputs. Now I need one additional step/direction servo for feeding material across the machine, this is the new axis (A1) which I need to add with the 7i78, and later there will be A2, A3, and A4 all working in the same way as A1 (but not in tandem like X1/X2, Y1/Y2). This new A axis does not require homing or any type of indexing, it simply does precision feeding on a single axis in either direction.

Currently I have referenced hm2_7i76e.0.stepgen.05.(commands) in the HAL file and cloned parts of my X axis for the new A axis in the INI file and I can not get linuxCNC to start and I am currently trying to understand the errors.

I would appreciate any help in pointing me in the right direction. I would love to help with setting up pncconf for the 7i78, I am not very good at coding as I am not a software engineer in any respect but I would be very glad to help or contribute in any way that is needed.
Last edit: 27 Sep 2019 00:57 by 5r100w. Reason: made error in loadrt line and changed A axis description to be more clear

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27 Sep 2019 02:28 #146318 by PCW

I did this with the assumption that because of the bitfile I have loaded, I can now manually add additional step generator/axis in HAL and INI file with HAL command like "setp hm2_7i76e.0.stepgen.xx.CC" where xx is additional step generators 05 thru 09 and CC are the setup commands for the axis but it does not work. I am reading the HOSTMOT2 manual but I can find little information about using the 7i78. I understand that this board just extends the P1/P2 connector of the 7i76e but I don't understand what I am doing wrong yet.


All stepgen hardware is the same other than the stepgen number so you can simply copy paste existing axis setup
and hal connections to add more jpints. pncconf created hal files use a PID component for local stepgen feedback
so you would also have to instantiate an additional PID component per added joint

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27 Sep 2019 03:17 #146321 by 5r100w
Thank you! I will proceed with creating the HAL and INI file and debug my errors in the morning.

I have another question, about the use of MIN_LIMIT and MAX_LIMIT under the axis configuration in the INI file: This A axis does not have limits; It feeds an unknown amount of material into the machine and will have a switch to indicate when the edge of the material has been reached (which will halt the machine). Can I create an axis with no limits by simply omitting MIN_LIMIT and MAX_LIMIT from the axis? It isn't clear to me yet in the documentation but I have only read it once and it is going to take a few reads for me to comprehend it all.

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27 Sep 2019 06:47 #146333 by pl7i92
you can use
MIN_LIMIT =9999
and MAX_LIMIT =9999
id your axis is in free run

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02 Oct 2019 04:59 #146856 by andypugh

pl7i92 wrote: you can use
MIN_LIMIT =9999
and MAX_LIMIT =9999
id your axis is in free run


Or bigger than 9999 if needed.

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