' =========================================================================
'
'   File....... Gray_To_Binary.BS2
'   Purpose....
'   Author..... Jon Williams -- Parallax, Inc.
'   E-mail..... jwilliams@parallax.com
'   Started....
'   Updated.... 17 DEC 2004
'
'   {$STAMP BS2}
'   {$PBASIC 2.5}
'
' =========================================================================


' -----[ Program Description ]---------------------------------------------


' -----[ Revision History ]------------------------------------------------


' -----[ I/O Definitions ]-------------------------------------------------


' -----[ Constants ]-------------------------------------------------------


' -----[ Variables ]-------------------------------------------------------

bVal            VAR     Nib
gVal            VAR     Nib
idx             VAR     Nib
idx2            VAR     Nib


' -----[ EEPROM Data ]-----------------------------------------------------

GTable          DATA    %0000, %0001, %0011, %0010,
                        %0110, %0111, %0101, %0100,
                        %1100, %1101, %1111, %1110,
                        %1010, %1011, %1001, %1000


' -----[ Initialization ]--------------------------------------------------

Reset:
  DEBUG CLS


' -----[ Program Code ]----------------------------------------------------

Main:
  DEBUG "Gray to Binary", CR, CR

  FOR idx = 0 TO 15
    READ (GTable + idx), gVal
    GOSUB Gray_To_Bin
    DEBUG BIN4 gVal, TAB, BIN4 bVal, TAB, DEC bVal, CR
  NEXT

  DEBUG CR, CR,
        "Binary to Gray", CR, CR

  FOR bVal = 0 TO 15
    GOSUB Bin_To_Gray
    DEBUG BIN4 bVal, TAB, BIN4 gVal, CR
  NEXT

  END


' -----[ Subroutines ]-----------------------------------------------------

Gray_To_Bin:
  bVal = gVal                                   ' copy high bit
  FOR idx2 = 2 TO 0                             ' process other bits
    bVal.LOWBIT(idx2) = bVal.LOWBIT(idx2+1) + gVal.LOWBIT(idx2)
  NEXT
  RETURN


Bin_To_Gray:
  gVal = (bVal >> 1) ^ bVal                     ' convert to Gray code
  RETURN 