7i92 with 7i77 Need Correct Firmware For Anti-phase PWM servo

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13 Oct 2019 04:08 #147784 by jsflanagan
I've got a SWI Prototrak that I'm trying to convert. I've got a 7i92 and 7i77, I've got the encoder input working I see it move when I rotate the servo. I'm having trouble getting the pwmgen configured properly. I've tried putting it in pwmgen type=2 but I can't seem to make it work for some reason. I know the drive is wired correctly as when I put a AAA battery across the PWM signal going to the servo drive it spins. So I know my issue is that I'm trying to drive the PWM single ended and I need to have a differential output. I've loaded my board with 7i92_7i77x2.bit from Mesa. Not sure if I've got the correct bit file or what I'm missing in my configuration. ini and hal files attached.
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13 Oct 2019 13:35 - 13 Oct 2019 13:37 #147817 by PCW
If you have PWM driven drives you need a different daughtercard.
a 7I77 is a +- 10V analog servo interface card. For drive controlled
by PWM/DIR or locked antiphase PWM you probably want a 7I76 or 7I85S
Last edit: 13 Oct 2019 13:37 by PCW.

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18 Oct 2019 23:56 #148249 by andypugh
But he says that a battery works, so it looks like an analogue voltage drive? A 1.5V battery seems like it should be too low to trigger a 5V PWM?

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19 Oct 2019 02:21 #148264 by PCW
Yeah hard to tell, as some analog drives are called PWM drives since the output is PWM

ISTR however that Prototrak uses differential PWM (with 50% = 0)

Ahh here's a relevant a thread

forum.linuxcnc.org/30-cnc-machines/29358...boards-mesa?start=20

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26 Oct 2019 02:02 #148807 by jsflanagan
ok I purchased a 7i76 and I am running it with the 7i92 along with my 7i77.

I have flashed 7i92_7i76_7I74D.bit but I need to order a cable to hook up the second board as I believe that I need to run both boards, the 7i77 for my encoder input, and the 7i76 for the differential PWM output to drive my servos. When I get the cable I think I need to hook the 7i76 to P1 and 7i77 to P2, is that correct the order of the names in the bit file defines which daughter board plugs into which port?

Second, reading thru the 7i76 manual it appears to be a step and direction board. What pin would I hook the +PMW and -PMW wires from the servo driver.

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26 Oct 2019 03:34 #148810 by PCW
Yes, firmware for the 5I25,6I25 or 7I92 usually has bitfiles named for the daughter cards
with the primary FPGA connector (P2 on a 7I92) daughter card listed first

The 7I76 just buffers the step/dir signals so they can be PWM/DIR signals as well with
appropriate firmware. I'm not sure there's existing firmware for this but I can build a bitfile
when I get a bit of free time, Do you know if Direction is needed for the PWM or is it 50% for
0 drive?

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