BCD to Integer instr. - STEP7

gumis · Apr 28, 2009

Hi all,

BCD to Integer instruction in STEP7 reads the contents specified in the input parameter as a three digit number in binary coded decimal format (BCD,+-999) and converts this number to an integer value. I understand that twelve less significant bits represents value and bit no.12 represents sign. Am I right?

My purpose is to convert eight bits ( MSB represents sign bit; bits:6,5,4 represent one BCD digit and 3,2,1,0 represent second BCD digit) to decimal value.

Could you give me some tip how to start up with this problem?

Regards,
gumis

L D[AR2P#0.0] · Apr 28, 2009

Here's the source code for an FC that will do the job:

Code:

FUNCTION FC 3 : INT
TITLE =
VERSION : 0.1

VAR_INPUT
  byData : BYTE ; 
END_VAR
VAR_TEMP
  bNegative : BOOL ; 
  byCopy : BYTE ; 
END_VAR
BEGIN
NETWORK
TITLE =
      L     #byData; 
      T     #byCopy; 
      LAR1  P##byCopy; 
      A      [AR1,P#0.7]; 
      =     #bNegative; 
      R      [AR1,P#0.7]; 
      L     B [AR1,P#0.0]; 
      BTI   ; 
      A     #bNegative; 
      JCN   plus; 
      NEGI  ; 
plus: T     #RET_VAL; 
END_FUNCTION

JesperMP · Apr 28, 2009

Quick and dirty with an intermediary word (MW10):

Code:

      L     0                           // clear intermediary word
      T     MW    10
      L     #byte_BCD                   // load original data
      T     MB    11
      A     M     11.7                  // move sign bit from byte to word address
      =     M     10.7
      R     M     11.7
      L     MW    10                    // convert to integer
      BTI   
      T     #word_integer

BCD to Integer instr. - STEP7

gumis

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L D[AR2P#0.0]

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JesperMP

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