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Hot!Hard-code Table Data In PIC18F Flash During Programming?

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jfriend
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2021/01/01 22:52:43 (permalink)
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Hard-code Table Data In PIC18F Flash During Programming?

I am writing a program in assembly. I've been reading the PIC18F67J60 datasheet about table reads and writes. No problems there. But suppose I want to hard-code some data into flash at program-time, not run-time. Is it possible to do this?
 
For example, let's say I want to send "MICROCHIP PIC18F67J60" over EUSART. To get the string, I could use the typical ADDWF PCL, RETLW routine, but that gets messy if I have a long string to send. It would be much cleaner and more efficient if I could write that string to flash during programming then simply use a TBLRD pointed to that string's location in flash.
#1

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    Equinoxin
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 15:59:54 (permalink)
    -1 (1)
    Hi have you looked into using the const type identifier for storing the table in flash? Please refer to the compiler manual for more information on using this. 
     
    #2
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:21:03 (permalink)
    +1 (1)
    rashmik
    Hi have you looked into using the const type identifier for storing the table in flash? Please refer to the compiler manual for more information on using this.

    OP is using assembly, not C.
    #3
    jfriend
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:21:15 (permalink)
    +2 (2)
    I have discovered how to do it, it is actually quite simple. First, indicate the origin point where you want it to be written in the ROM:
     
    ORG 0x???? ;example ORG 0x0800
     
    Following that directive, add the hard-code using any number of methods:
     
    lbl_single DATA "M","C","U" ;creates three separate words of 004Dh, 0043h, and 0055h
    lbl_double DATA "MCU" ;creates two words of 434Dh and 0055h, the last one padded with "0"s
    lbl_hex DATA 0xffff,0xaa55; creates two words in that exact order
     
    For the PIC18, the first character is the least significant byte. Writing DATA "MC" will actually write "CM", which will be read that way when using a sequential table read. So when writing data by hand, it must be remembered to swap the two bytes.
    #4
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:21:30 (permalink)
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    jfriend
    I am writing a program in assembly. I've been reading the PIC18F67J60 datasheet about table reads and writes. No problems there. But suppose I want to hard-code some data into flash at program-time, not run-time. Is it possible to do this?
     
    For example, let's say I want to send "MICROCHIP PIC18F67J60" over EUSART. To get the string, I could use the typical ADDWF PCL, RETLW routine, but that gets messy if I have a long string to send. It would be much cleaner and more efficient if I could write that string to flash during programming then simply use a TBLRD pointed to that string's location in flash.

    Which assembler? MPASM or PIC-AS?
     
    #5
    jfriend
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:23:35 (permalink)
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    MPASM.
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    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:29:00 (permalink)
    +3 (3)
    jfriend
    MPASM.

    jfriend
    For the PIC18, the first character is the least significant byte. Writing DATA "MC" will actually write "CM", which will be read that way when using a sequential table read. So when writing data by hand, it must be remembered to swap the two bytes.

    These are the same:
            data    "CHIP"

            db      "CHIP"

            db      'C', 'H', 'I', 'P'

    post edited by 1and0 - 2021/01/15 16:31:37
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    jfriend
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:46:20 (permalink)
    0
    That is correct for PIC16 devices. PIC18 is not the same. I have successfully programmed hard data into ROM and can verify it must be written in 0x3412, 0x7856 format using DATA.
     
    Your first two examples will write 0x4843, 0x5049. That equates to "H", "C", "P", "I" if you read them sequentially.
     
    The last "db" will write 0x4300, 0x4800, 0x4900, 0x5000.
     
    From MPASM help file:
    "On all families except the PIC18 device family, the first character is in the most significant byte of the word. On the PIC18 device family, the first character is in the least significant byte of the word."
    post edited by jfriend - 2021/01/15 16:51:15
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    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 16:59:43 (permalink)
    +2 (2)
    jfriend
    That is correct for PIC16 devices. PIC18 is not the same. I have successfully programmed hard data into ROM and can verify it must be written in 0x3412, 0x7856 format using DATA.
     
    Your first two examples will write 0x4843, 0x5049. That equates to "H", "C", "P", "I" if you read them sequentially.
     
    The last "db" will write 0x4300, 0x4800, 0x4900, 0x5000.
     
    From MPASM help file:
    "On all families except the PIC18 device family, the first character is in the most significant byte of the word. On the PIC18 device family, the first character is in the least significant byte of the word."

    Let me repeat again, the followings
        data    "1234"
        db      "1234"
        db      '1', '2', '3', '4'

    will generate the SAME opcodes of
        0x3231
        0x3433

    on a PIC18 device.
    #9
    jfriend
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 17:22:20 (permalink)
    0
    I have not tried "db" specifically, I have only read the information from MPASM help file. According to that, your first two examples are correct but the last one will not produce the same result on a PIC18 device. Again, the help file:
     
    Example 2: PIC18 Devices
    db "t", "e", "s", "t", "\n"
    ASCII: 0x6574 0x7473 0x000a


    Are you saying this example from the help file is wrong?
    #10
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 17:46:47 (permalink)
    +2 (2)
    jfriend
    I have not tried "db" specifically, I have only read the information from MPASM help file. According to that, your first two examples are correct but the last one will not produce the same result on a PIC18 device.

    Why don't you try it and see for yourself?
     
    jfriend
    Again, the help file:
     
    Example 2: PIC18 Devices
    db "t", "e", "s", "t", "\n"
    ASCII: 0x6574 0x7473 0x000a


    Are you saying this example from the help file is wrong?

    It is correct.

    't'  -> 0x74
    'e'  -> 0x65
    's'  -> 0x73
    't'  -> 0x74
    '\n' -> 0x0A

    so, the opcodes are
     
    0x6574 0x7473 0x000A
       e t    t s     \n
    #11
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 17:55:48 (permalink)
    +2 (2)
    In another view,

    't'  -> 0x74  <- lower byte
    'e'  -> 0x65  <- upper byte
    's'  -> 0x73  <- lower byte
    't'  -> 0x74  <- upper byte
    '\n' -> 0x0A  <- lower byte
            0x00  <- upper byte, odd number of bytes padded with 0x00
    #12
    ric
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 20:22:00 (permalink)
    +1 (1)
    jfriend
    I have not tried "db" specifically, I have only read the information from MPASM help file. According to that, your first two examples are correct but the last one will not produce the same result on a PIC18 device. Again, the help file:
     
    Example 2: PIC18 Devices
    db "t", "e", "s", "t", "\n"
    ASCII: 0x6574 0x7473 0x000a


    Are you saying this example from the help file is wrong?

    You are getting yourself confused by jumping between byte views and word views.
    Stop looking at what the word looks like in memory, and it all cancels out.
     

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
    To get a useful answer, always state which PIC you are using!
    #13
    teenix
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/15 23:29:54 (permalink)
    +1 (1)
    Hi,
     
    This is pretty basic demo assembler for 18Fxxxx
     
    doStrXmit
        movlw UPPER str_Test
        movwf TBLPTRU
        movlw HIGH str_Test
        movwf TBLPTRH
        movlw LOW str_Test
        movwf TBLPTRL
    strLoop    tblrd*+
        movf TABLAT,W
        btfsc STATUS,Z      ; is data 0?
        return                   ; yes
     
        call doXmit             ; send Wreg to USART, assumes waits until data sent
        bra strLoop
     
    ; somewhere in ROM
    str_Test
        data "MICROCHIP PIC18F67J60", 0x000D    ; + CR and 0 string terminator
     
    cheers
     
    Tony
    #14
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/16 10:09:46 (permalink)
    +2 (2)
    teenix
    strLoop    tblrd*+
      movf TABLAT,W
      btfsc STATUS,Z      ; is data 0?
      return                   ; yes
     
      ; snipped
    str_Test
      data "MICROCHIP PIC18F67J60", 0x000D    ; + CR and 0 string terminator

    That will not work as expected for string with an odd number of characters, which your string is. It is better to use escape characters which are also self documenting:
        data "MICROCHIP PIC18F67J60\r\0"

     
    #15
    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/16 11:54:35 (permalink)
    +2 (2)
    DB directive works too:
        db  "MICROCHIP PIC18F67J60", 0x0D, 0


    I'd prefer to use the DB directive like this:
        db  "MICROCHIP PIC18F67J60\r\0"

    post edited by 1and0 - 2021/01/16 12:25:05
    #16
    teenix
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/16 21:27:38 (permalink)
    0
    Thanks for the heads up, I miss-counted the characters.
     
    Still, on the positive side, it is a example of errors that can occur.
     
    cheers
     
    Tony
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    1and0
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    Re: Hard-code Table Data In PIC18F Flash During Programming? 2021/01/16 21:52:23 (permalink)
    +1 (1)
    teenix
    Thanks for the heads up, I miss-counted the characters.
     
    Still, on the positive side, it is a example of errors that can occur.

    I rarely use the DATA directive. I prefer to use the DB directive for Bytes and DW directive for Words, meaning no need to count. ;)
    #18
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