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Shorthand syntax questions. Having trouble — Parallax Forums

Shorthand syntax questions. Having trouble

zongozongo Posts: 2
edited 2009-09-23 13:10 in Propeller 1
Hello All,

I have attached a file that can also be found at

http://obex.parallax.com/objects/138/


I set up the circuit and it works just fine, but now I want to understand the programming.


The attachment is a bundle of files from the obex file cited above. (I included them all because it might help someone answer my question.)

The specific file that contains code lines I cannot understand is the file

CD_LTC1298.spin


These code lines are part of a repeat loop, but I just have the offending lines here so you can see what I mean.


datar |= |< i ' set bit i HIGH

datar &= !|< i ' set bit i LOW


Is that shorthand?

If so, can someone tell me what the "longhand" would be for an equivalent statement?

I think it says something about comparing "datar" with ORs and ANDS, and then doing some bitwise operations but I am lost from there.

I do know that the loop this code is located spits out the 12bit ADC data from each channel from a 2-channel ADC.

Thanks,

zongo
zip
zip
CD_LTC1298.zip
35K

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-09-21 23:37
    datar |= |< i is the same as datar := datar | (1 << i)

    datar &= !|< i is the same as datar := datar & !(1 << i)

    -Phil
  • SamMishalSamMishal Posts: 468
    edited 2009-09-21 23:41
    Hi Zongo,

    datar |= |< i ' set bit i HIGH
    datar &= !|< i ' set bit i LOW


    The |=·operator (Or-Assign) does two things it ORs the left operand with the right operand
    and then it assigns the result to the left variable.

    So datar |= 5·· will OR datar with the number 5 and the result will be put back into the
    variable datar.

    now the |< operator·puts a 1 in·one of the·bits of a 32-bit number Zero. Which bit is defined by the number on the right
    of the operator. So when you say |< 9 then you will have a 32 bit number with all Zeros in all bits except in bit 9.

    so datar |= |< i

    will create a number with all bits of 0 except the ith bit set to 1
    it will then OR datar with that number
    it will then put the result back into datar

    The resulting outcome is that the ith bit in the value of the number stored in the variable datar has been turned ON.

    The next line is doing a similar thing but it ANDs (the &= is the AND-Assign operator) the ith bit with a 0 which turns it off.
    This is achieved by inverting the result of the |< i· using the ! operator which is called the NOT operator which basically
    inversts all the bits of the number.

    So then if we·invert a 32 bit number with all bits as 0 except for the ith bit, we end up with a number with all the
    bits as 1 except for the ith bit as 0.

    Remember when you OR with 1 you get 1· and when you AND with 0 you·get 0.

    Regards

    Samuel



    Post Edited (SamMishal) : 9/23/2009 5:34:50 AM GMT
  • zongozongo Posts: 2
    edited 2009-09-22 06:56
    Thank you so much sirs!

    This may be exactly what I need.

    Oh, Anyone know of a quick reference guide that has good, concise synopses on shorthand (the commands...a single example for each, etc.)?

    Currently reading the manual and PE Fundamentals, but the closest thing to what I want is the parallax Quick Reference for spin and assembly. All are very helpful, but not the distillation I need.

    Thanks again, I can now continue figuring the rest of the method.

    zongo
  • KMyersKMyers Posts: 433
    edited 2009-09-22 22:05
    ZONGO, thanks for posting your question. I was confused on this also. It makes sense somewhat now so I guess its time
    to play!

    Ken
  • SamMishalSamMishal Posts: 468
    edited 2009-09-23 05:24
    Hi Zongo,

    The best reference to all the operators and a VERY GOOD description of how they
    work etc. is in the Propeller Manual. Section called Operators on Page 143 to 174 of
    the version 1.1 manual.

    It is 32 pages of GOOD information and the table given on page 144 and the other
    on page 145 are good quick reference you should copy them and put them in a handy
    place for Quick Reference.

    I think once you read these 32 pages you should be OK.

    Regards

    Samuel



    Post Edited (SamMishal) : 9/23/2009 5:34:37 AM GMT
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-09-23 06:14
    These shorthands were designed by C programmers to confuse ordinary persons from understanding their code LOL

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Links to other interesting threads:

    · Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-09-23 07:10
    I agree with Cluso. Except for the LOL bit *grin*

    One of the things I really like about the prop is the mix n match with spin/machine code. Coming from a Z80/8080/Pic background, I find machine instructions easier to understand but that is just a personal preference. It is amazing what you can do with just 4 prop machine instructions -
    AND ' logical and
    OR ' logical or
    SHL ' shift left n bits
    SHR ' shift right n bits

    I find these instructions self explanatory, although it never hurts to have the binary values before and after as a comment.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    www.smarthome.viviti.com/build
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-09-23 07:32
    It was always said C was invented by programmers who hated non programmers being able to understand their basic and pascal programs.
    Sometimes I think there is more truth in this than I would like to believe.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Links to other interesting threads:

    · Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • jazzedjazzed Posts: 11,803
    edited 2009-09-23 13:10
    You guys are so funny. Ordinary people should be watching football instead of writing code [noparse]:)[/noparse]

    I started writing a book called Supermodel Programming. I figured if I could teach a Supermodel (Tyra Banks, etc...) how to program, I could teach anyone. My daughter pointed out that Supermodels wouldn't even be thinking about writing programs, so I would be wasting my time ... I reluctantly agreed.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    --Steve

    Propeller Tools Post Edited (jazzed) : 9/23/2009 1:22:27 PM GMT
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