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Re[2]: HELP - pushing Inferno as a solution


  >i forwarded the two messages talking about ladder logic 
  >to a friend who's been working on ladder logic 
  > compilers, and this was his reply.
  > rog.
 >  .............
 >- due to lack of procedures, if you want to do the same thing 
 > 1000 times, you write it 1000 times...
 This is only true in the sense that  subroutines of ladder 
 logic does not support the concept of "local variables". 
 However, by using ladder logic (similar to 
 using any low level language),  
 a programmer can implement  those things by himself. For
 example, one of my friends wrote a recursive program in ladder
 logic (Of course, he  implemented stack by himself).  
> ..........................
>The problem with the IEC-1131 system is that they still 
>interpret a PLC to be scan-based, which isn't going to do much
> good if you want to program your control system in limbo. .....

I am not sure this is really the problem of IEC-1131-3 . I think 
that the interpretation of PLC being scan-based comes from the
fact that OS in PLC works that way. 

The key issue here is not languages but real-time OS'. If 
controllers use Inferno kernel to replace its own native OS,  
people can not only
 write industry control programs in limbo,but also  write  in 
ladder logic if they wish. (It's doable to write a ladder logic 
compiler on Inferno). The advantage by using Inferno is not just
make programmers' life easier. 
In fact, from CS point of view, an industry control system 
consisting various programming controllers is a distributed 
computing system. Currently PLC protocols&OS&ladder programs(even 
plus IEC-1131-3 programs) cannot handle such kind of system 
properly. One thing is for sure, 
soon or later, whether or not it is Inferno, some new networking 
real-time OS will change the current PLC technology. 
> ..................................
>All opinions are mine, and have no relation to those of my employer.
     All opinions are mine, and have no relation to those of my employer.
     Jianan Li