On Monday 17 December 2018 06:09:51 andy pugh wrote: > Not as on-topic as I would like, but I suspect that some of you here > might know something useful. > > I am trying to interface an ADS1256 board to an Arduino. > https://www.ebay.co.uk/itm/19242863594 > > Sometimes it almost works... > It will often sit there reading all-zeros then suddenly appear to > work, to an extent. But I don't seem to be able to configure it for > single-ended so suspect that the programming instructions are not > getting through. > The fact that the data output comes and goes makes me suspect that the > SPI comms is iffy. > > The connection runs via the IO pins of an Arduino Nano,rather than > using the ICSP connector. > > If I touch the ICSP connector on the Nano with my finger then the data > switches to 0xFFFFFF > > So, I am wondering if the SPI bus needs to be terminated or something? > Generally, its src terminated with a 120 ohm chip r as close to the arduino as you can get it.
The spi bus is a different critter and generally works best when its running fast enough to lose the squarishness of the wave. And its very finiky about rise and fall times since it uses the data slew rates for its clocking. Often working better if its capacitively loaded just to slow the rise and fall of the waveform data. I'm running a medium sized 70 yo Sheldon lathe with an spi addressed mesa 7i90D interface from a raspi 3b. The raspi is writing to the 7i90 at 42 megabaud, the reading its responses at 25 megabaud, and working flawlessly over a 2" piece of 26 pin ribbon. At those speeds, even 2" is a transmission line and has to be treated as such. > Also, the board has 100 Ohm resistors in series with all digital IO, > but the ADS1256 data sheet only shows 100R resisitors on the input > channels. Is this likely to be worth changing? Probably not, the internal r of the gpio driver will be enough to make a decent 1GHz digital scope on the spi signals would show whats going on, or might even make > > I have used other SPI devices with the Nano, and have not had these > problems. I have also tried with a full-size Arduino, with equally > limited success. > > Any tips for robustification of SPI comms? See above, I'm still learning what works myself. -- 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> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
