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  1. #1
    Join Date
    Jul 2013
    Posts
    28

    Default Sending multiple serial strings.

    Hello,

    What is the best way to save and send multiple strings via serial?

    I need to send motion commands to a stepper motor controller. Each command (Stop, Left, Right, etc.) is comprised of (8) Hex codes. These are sent TTL 9600BPS, 8N1.

    My thought was to save each of these to a VAR (which could be a constant?) and then reference each when calling HSEROUT.

    ' Instead of directly:
    HESEROUT [HEX 55, AA, 1, FF, 0, 0, AA, 56]

    ' Use something like this:
    HESEROUT [mcuStop]

    Although directly works fine, it is quite awkward when creating elaborate motion profiles.

    I am not sure how to store these strings as VAR's/Array's/Tables or how to call them?

    Thanks!


    ' Partial list of about 24 commands.
    mcuStop = [HEX 55, AA, 1, FF, 0, 0, AA, 56]
    mcuCoast = [HEX 55, AA, 12, EE, 0, 0, AA, 56]
    mcuForward = [HEX 55, AA, 3, FD, 0, 0, AA, 56]
    mcuReverse = [HEX 55, AA, 4, FC, 0, 0, AA, 56]
    mcuLeft = [HEX 55, AA, 5, FB, 0, 0, AA, 56]
    mcuRight = [HEX 55, AA, 6, FA, 0, 0, AA, 56]
    mcuSpeed1 = [HEX 55, AA, 17, E9, 0, 0, AA, 56]
    mcuSpeed2 = [HEX 55, AA, 1A, E6, 0, 0, AA, 56]
    mcuSpeed3 = [HEX 55, AA, 18, E8, 0, 0, AA, 56]
    mcuSpeed4 = [HEX 55, AA, 19, E7, 0, 0, AA, 56]

  2. #2
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,264

    Default Re: Sending multiple serial strings.

    Hi,
    One way to do what you're asking for is something like
    Code:
    mcuStop VAR BYTE[8]   ' Array of 8 bytes
      mcuStop[0] = $55
      mcuStop[1] = $AA
      mcuStop[2] = $01
      mcuStop[3] = $FF
      mcuStop[4] = $00
      mcuStop[5] = $00
      mcuStop[6] = $AA
      mcuStop[7] = $56
    
    HSEROUT [STR mcuStop]
    However, with 24 commands, each consisting of 8 bytes you're going to "waste" 152 bytes of RAM on this - which may or may not matter.

    Another aproach would be to create 24 subroutines and call them using GOSUB
    Code:
    mcuStop:
      HESEROUT [$55, $AA, $01, $FF, $00, $00, $AA, $56]
      RETURN
    
    mcuCoast:
      HSEROUT [$55, $AA, $12, $EE, $00, $00, $AA, $56]
      RETURN
    
    GOSUB mcuStop
    GOSUB mcuCoast
    Yet another posibillity might be the user command feature in PBP3 but that's a quite advanced feature.

    It looks like all of the commands starts and ends with the same sequenct of bytes, 55, AA, xx, xx, 00, 00, AA, 56 where xx are the actual data. Is that valid for all commands?

    /Henrik.


    55, AA, 1, FF, 0, 0, AA, 56

  3. #3
    Join Date
    Jul 2013
    Posts
    28

    Default Re: Sending multiple serial strings.

    Option 1 is quite logical.
    Why does it "waste" RAM? Could it be stored in ROM instead?
    Option 2 is simple.
    In composing the moves, I do want to avoid typing those long strings over and over.
    Good observation.
    Each packet does have the same beginning and end. (55, AA and then AA, 56)
    The four bytes in between is the payload.

  4. #4
    Join Date
    Jan 2005
    Location
    Montreal, Quebec, Canada
    Posts
    2,254

    Default Re: Sending multiple serial strings.

    Henrik is right. You can then tweak his approaches to use headers (prefix codes) and footers (suffix codes).

    Robert


    Edit: "waste" is relative. It depends on your PIC, program size and variables used. If you have little codespace, option 1 might be better.

    If you "have" to use memory and you have little left on the PIC, is I/O time to external storage a concern?

    It all depends on your PIC, application requirements and personal preference.
    Last edited by Demon; - 26th September 2014 at 23:33.

  5. #5
    Join Date
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    Location
    Sweden
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    Default Re: Sending multiple serial strings.

    Hi,
    Why does it "waste" RAM? Could it be stored in ROM instead?
    Waste may not have been the best word. What I mean is that the string for each command is static, they don't change, so there's no real need for them to live in RAM - which they'll do if you follow option 1 in my previous post. Again, there's nothing inherently wrong with this and it might be the easiest way if you have the RAM to spare.


    It IS stored in ROM (FLASH actually) when you do it like
    Code:
    HESEROUT [$55, $AA, $01, $FF, $00, $00, $AA, $56]
    Which means that option 2 does, obviously, use less amount of RAM.

    With PBP3 there are ways to create unique usercommands but it's a pretty advanced topic. With the information given so far I'd go for option 2. Create a subroutine for each of the 24 commands and call them in sequence using GOSUB.

    /Henrik.

    EDIT: And if you DO go for option 2 and want to save some codespace you could probably do that by creating a "send header" and a "send footer" sub so you don't need to store the same 4 bytes for each command 24 times.
    Code:
    mcuStop:
      GOSUB SendHeader : HESEROUT [$01, $FF, $00, $00] : GOSUB SendFooter
      RETURN
    
    SendHeader:
       HSEROUT [$55, $AA]
       RETURN
    
    SendFooter:
       HSEROUT [$AA, $56]
       RETURN
    EDIT2: And now, if you use an 18F part and have LONGs enabled you COULD possibly do something like:[code]
    Code:
    Header CON $55AA
    Footer CON $AA56
    MotorStop CON $01FF0000
    
    mcuStop:
      GOSUB SendHeader : HESEROUT [MotorStop] : GOSUB SendFooter
      RETURN
    
    SendHeader:
       HSEROUT [Header]
       RETURN
    
    SendFooter:
       HSEROUT [Footer]
       RETURN
    Watch out for Little vs big endian, I'm not sure, off the top of my head how it's being sent here so you may need to reverse it.
    Last edited by HenrikOlsson; - 27th September 2014 at 11:03.

  6. #6
    Join Date
    Jul 2013
    Posts
    28

    Default Re: Sending multiple serial strings.

    Yet another approach would be create mcuCMD array and just dynamically change interior bytes to a specific motion command.

    Boy, lots of options!
    Thanks for getting me started!

    For the immediate, I am going with Option 2 using the 24 GoSubs which is both pretty efficient and easy to read or maintain.

    Z

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