On 5/12/2013 3:39 AM, Lars Andersson wrote: > On 5/11/2013 3:52 PM, Andrew wrote: >> An IO pin can be connected unless there’s an OUT pin on the signal >> >> An OUT pin can be connected only if there are no other OUT or IO pins on >> the signal" >> >> >> Regards, >> Kent > Yes, > I have read that too. I fail to understand what is the meaning of an IO > pin? It is no different from an OUT pin. > >
I admit I struggled to wrap my brain around this notion when I first read the LinuxCNC docs. Syntactically, there is a difference in these pin types simply because the parsing rules in halcmd say there is a difference. In particular, the two rules quoted above mean two or more OUT pins can never be connected together by a signal, two or more IO pins can, or one OUT pin and one or more IO pins can. Semantically, the difference is conditional on the internals of the components involved. A quick grep of the src/hal/components directory shows the pin-direction definition "HAL_IO" occurs in 13 component files, pid.c included. I haven't studied how the IO-pin type is used in each, nor have I studied carefully different HAL configurations which use these particular components. Consequently, I can't say whether this HAL analog to tri-state logic is essential or merely convenient. Regards, Kent ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
