On Friday 09 December 2016 12:23:49 Peter C. Wallace wrote: > On Fri, 9 Dec 2016, Gene Heskett wrote: > > Date: Fri, 9 Dec 2016 12:05:42 -0500 > > From: Gene Heskett <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > <[email protected]> > > To: [email protected] > > Subject: [Emc-users] Need advice on joint errors > > > > Greetings all; > > > > I could use some advice since this raspi-7i90 uses a com protocol, > > spi, that is relatively new, and I believe that is where a noise > > problem might lie. > > > > I got it back to running the right rt kernel yesterday, and I am > > waiting on another psu & driver for the x axis. But I did get z > > moving. Nowhere near optimized though. That's being moved by the > > motor and psu I took off the mill because it was too slow. > > > > But I am being plagued by joint following errors, both axis's, when > > its not moving. There is not any connections yet to the x motor pins > > on the 7i90. > > > > This armhf setup has no PID's, so I've yet to locate where this > > error is generated. > > > > My hookup for the spi is currently some of those rip off the next > > wire and plug it in, and each is a piss-poor connector, very poor > > spring pressure unless I first take a tiny punch and bend the > > contact tab inward so it will even stay on the header pin. I've seen > > some mention of 80 ohm series damping resistors, but this initial > > hookup is straight thru, and a bit shy of 200mm long. At the speed > > of this interface, it really should be treated as a transmission > > line, but its not a very good one when its all done with loose > > wires. > > > > I got some of the 10 pair female connector blocks from digi-key > > yesterday, and the gold flashed female pins, and the crimping tool > > came in Tuesday, so I think the first thing I'll do today, is cut > > those junk connectors of these jumpers, and make it back up using > > these good connectors. That will shorten each wire something under > > an inch. It also gives me a chance to put some damping resistors in > > the signal lines, possibly cutting down on the ringing and the data > > errors that I'm convinced is the source of the joint errors being > > reported when there is not any motion. > > > > So my question is, are 100 ohm R's, which I have in bulk, too much? > > > > The one mention was of 80 ohm chip R's on the OHPark adaptor board I > > assume, which puts them right on the r-pi's header, but when the > > door of this box is closed, I don't have room for any additional > > stickup above the r-pi, but the interface on the 7i90 faces straight > > out, so putting them there, on the other, 7i90 end, is quite easily > > done. > > > > I'm also aware this is new ground, so what have the explorers here > > found is the best solution for an spi driven setup? > > > > Did you use loose jumpers, or did you use a ribbon cable, arranged > > to put a grounded wire between the signal wires? I have around 80 > > feet of 26 wire ribbon cable, so thats not a problem. > > > > The pin pattern on the r-pi is easily covered by one, or a piece of > > one of these header blocks I have now. > > > > Using ribbon cable makes it a lot easier to think of it as a > > transmission line, but how best to terminate it for least vswr? > > > > So lets talk. > > > > Thanks everybody. > > > > Cheers, Gene Heskett > > The SPI pinout is designed to use flat cable which has interleaved > grounds. any flying wire interface is liable to be troublesome > > There are 2 issues here, 1. Is controlled impedance (the flat cable > has ~!30 ohm single ended impedance) and 2. Is ground bounce (you want > as many grounds between the 7I90 and the SPI master to avoid ground > bounce, 8 are available on the flat cable) > But the nice neat, all in a row on the 7i90 are not all in a row on the R-Pi 3b.
And I could have sworn I had some 26 pin header females that would fit the the 7i90. Could not find them so I cut a longer cable that didn't work so just fine when I made it. So I cut off about 10", visualized it laying back over the top of the 7i90 for about an inch before being folded at 90 degrees so it stuck strait up to put the red wire into the lowest pin I needed on the R-Pi's 40 pin, then cut pin 1 loose at the 7i90 because I don't need the VCC to power the 7i90 or the r-pi. So I am merrily (not really, loading this crimper is a PITA) marching along installing the connectors, until I get to the 7i90's pin 18. Continuity to the edge of the cable sticking out from under the holddown cap, but not at the other end of a perfectly undamaged cable 9" away. Took it apart, cut off the idc piercing and re-installed it. Still no continuity, start checking beyond pin 17, 19, 20 etc. No continuity beyond pin 16, and there is zero physical damage. I originally cut that piece off my 100 foot roll 2-3 years ago to make a breakout cable for TLM so I could make the home switching a little more intelligent. Couldn't make it work then, and now I know why. So digi-key, here I come asking for another 10 back of that IDC connector. I should have the psu and motor driver for X tomorrow. If nothing else pull some 12/3 w/g Romex into the conduit I finally have ready so I can get the 254 volt feed I was test-powering the vfd, off the floor. By now my back is done is done for the day, so tomorrow I cut another foot off my roll of 26 wire ribbon. and test every wire before I waste time & connector inserts trying to make another jumper cable. I swear, that Murphy that wrote all those laws is in residence here. That turkey even drank my last near beer about 2 weeks back and didn't even leave a thank you note. > Also regards grounding, you need to watch out for ground loops that > let high frequency noise currents flow between the 7I90 and the CPU. > > The most critical signal is the clock from the SPI master. And what is that signal labeled. The hookup docs Matshe sent me do not completely match the labels in the interconnection diagram. One signal has a / in front of it, so I am assuming thats it because nothing else would be true/low and make sense. If anyone here has taken the time to figure out whats the best way to plug the pins into a 10 pair female, so we just drop that onto the R-Pi header, x number of positions offset, and I am thinking the top end ought to hit the R-Pi's pin 30 (its highest ground) and work down, but posting that here would help to std-ize how we do this in the future. There are not enough grounds on the R-Pi to grab the 8 available on the 7i90. > depending > on the drive strength it may require a series termination resistor > (the 7I90 SPI output are series terminated so need no termination ) Thanks Peter. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/xeonphi _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
