On Thursday 04 May 2017 13:47:22 Chris Albertson wrote: > On Wed, May 3, 2017 at 11:32 PM, Erik Christiansen > <dva...@internode.on.net> > > wrote: > > On 03.05.17 22:40, Gene Heskett wrote: > > > On Wednesday 03 May 2017 22:29:43 Chris Albertson wrote: > > > > RS422 is balanced and opt isolated at the Mesa card end so you > > > > likely have better noise resistance then with SPI. > > > > > > rs485 is the single ended cousin. Could a atom board keep up with > > > that with a pci-e rs422 card in it? That does have a bit of an > > > attraction, particularly from the noise safety dept. Silly Q: can > > > the pi do rs422 over its gpio? > > > > Hook a RS485/RS422 transceiver to a Pi's serial TXD & RXD, and > > terminate each end of the twisted pair cable in 120 ohms, then it's > > done. All the chip does is TTL/CMOS to differential Tx & Rx. > > What is the maximum bit rate of the Pi's serial TXD & RXD? The 7i90 > can accept RS422 up to 10M bits/second. Can the Pi take advantage > that? Certainly an Intel PC could, > I don't see why not. The spi runs with a 32 megahertz clock, thru 4 gpio pins. Its a half-duplex protocol.
> Yes I agree conversion is cheap and easy, You can buy the Max chips > on breakout boards with connectors for 50 cents each > ebay.com/itm/2PCS-MAX485-Module > <http://www.ebay.com/itm/2PCS-MAX485-Module-RS-485-Module-TTL-to-RS-48 >5-Converter-For-Arduino/131694536431?_trksid=p2047675.c100005.m1851&_tr >kparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40130%26meid%3De5 >19e5e6252c4e40b7d0fa2b19dcd5fc%26pid%3D100005%26rk%3D6%26rkt%3D6%26meho >t%3Dag%26sd%3D112076449800> In most cases it is best to buy the chips > on boards with connectors. Saves you from a lot of work. > I agree. The only problem with this board is that its rs485 only. Unbalanced IOW. So theres goes some of the noise margin. And its data rate must be pretty slow, its slew rated but not in any usefull way. > People are using Cat5 (Ethernet cable) for all types of serial links > now. It just works better as most links are now balanced pairs. > > > I bought some surplus DS3695A RS485/RS422 half-duplex transceivers a > > few days ago for US30c each, but they draw over 27 mA, idling, - a > > MAX485 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
