Gray code was (is) very important in mechanical absolute decoding to avoid false codes if the switches are not perfectly aligned. One example is aircraft decoding altimeters where the code wheel can turn really slowly.
-----Original Message----- From: Peter blodow [mailto:p.blo...@dreki.de] Sent: den 11 mars 2009 22:45 To: Enhanced Machine Controller (EMC) Subject: Re: [Emc-users] 24 Position Absolute Encoder Hello all, Gray code is not primarily meant for mechanical switches, but for asynchronous counters. In the case of adding 1 to, say, binary 1111 1111, all the bits have to switch, one after the other, to yield 1 0000 0000 which, in the asynchronuos case, takes 8 times the time of a single carry operation. Imagining a 24 bit counter this can amount to a very large amount of time with the risk of losing counts in the meantime. So, the maximum count frequency depends on wether a carry operation is due or not. The Gray code avoids this at the cost of an odd and rather unusual decoding scheme. Greetings form Germany Peter Blodow At 07:39 10.03.2009, you wrote: >On Tue, 2009-03-10 at 01:54 -0400, Stephen Wille Padnos wrote: >... snip > > To do that, you need to use weighted_sum. > > There is no gray code converter at the moment, though it should be > > pretty easy to write one. > > > > - Steve > >Steve: Oops, your right, I used weighted_sum on my Hardinge tool >changer. >... >### TURRET ### ># create signals for tool loading loopback >linkpp iocontrol.0.tool-prepare iocontrol.0.tool-prepared >linkpp iocontrol.0.tool-change turret.0.position-change >linkpp turret.0.position-changed iocontrol.0.tool-changed > ># decode turret encoder inputs >net ones ppmc.0.din.06.in wsum.0.bit.0.in >net twos ppmc.0.din.07.in wsum.0.bit.1.in >net fours ppmc.0.din.08.in wsum.0.bit.2.in >net eights ppmc.0.din.09.in wsum.0.bit.3.in ># wsum.N.hold bit in > >net TurretCurrentPosition wsum.0.sum turret.0.position-current >net TurretRequestedPosition iocontrol.0.tool-prep-number >turret.0.position-requested >... > > >I checked out gray code on wikipedia and the advantage of gray seems to >be with using mechanical switches to sense position. With gray, you >don't need to wait for switches to settle to get a valid code, since >only one switch changes between positions. I'll be using clock bits to >control when the bits get read, so I'm tending toward using binary, or >the magnetic analog sensor. >----------- >Kirk >http://www.wallacecompany.com/machine_shop/ > > > >--------------------------------------------------------------------------- --- >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users ---------------------------------------------------------------------------- -- Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are powering Web 2.0 with engaging, cross-platform capabilities. Quickly and easily build your RIAs with Flex Builder, the Eclipse(TM)based development software that enables intelligent coding and step-through debugging. Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are powering Web 2.0 with engaging, cross-platform capabilities. Quickly and easily build your RIAs with Flex Builder, the Eclipse(TM)based development software that enables intelligent coding and step-through debugging. Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
