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From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: forth eng./68hc11 new micros
Message-ID: <599.UUL1.3#5129@willett.UUCP>
Date: 2 Mar 90 03:56:39 GMT
Organization: Latest link in the ForthNet chain.  (Pgh, PA)
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 Date: 03-01-90 (00:48)              Number: 404 (Echo)
   To: ALL                           Refer#: NONE
 From: JACK BROWN                      Read: (N/A)
 Subj: FORTH SOLUTION TO 1C          Status: PUBLIC MESSAGE

 ( 68hc11 Assembly Language Programming Course                     )

 ( Problem 1c )
 ( Write a 68HC11 assembly language program which will find the    )
 ( largest of 10 numbers stored in contiguous memory locations     )
 ( starting at location $0020. The numbers are single byte         )
 ( unsigned integers.  Save the largest number in memory at        )
 ( location $002A.                                                 )

 ( Solution 1c )
 ( Since we have no free memory at $0020 we will use memory at $90 )
 ( and location $9A for the largest number.                        )

 ( Find the maximum of 10 bytes located at $90,  max at $9A        )

 HEX
 0090 CONSTANT DATA  ( Location of byte array of data )
 009A CONSTANT MAXI   ( Location to save maximum value )
 000A CONSTANT N     ( Size of byte array             )

  DATA N 22 FILL      ( Some test data )
   88  DATA 5 + C!    ( 88 should end up at 9A )
    0  MAXI C!


 ( High Level Forth Solution :                                     )
 ( : MAXIMUM  ( -- )
 (       0 10 0 DO  DATA I + C@ 2DUP  <                            )
 (                  IF   SWAP THEN DROP                            )
 (            LOOP  MAXI C! ;                                      )


 ( Typical assembly language solution to the maximum problem       )
 CODE MAXIMUM  ( -- )
                 CLRA,  ( set maximum to zero )
         N    #, LDX,   ( set byte array size in X )

 BEGIN,
         DATA ,X CMPA,  ( max - data )
                 U<,
 IF,
         DATA ,X LDAA,  ( Save current as maximum )
 THEN,
                 DEX,   ( Point to next item in byte array )
                 0=,    ( Continue until all have been checked )
 UNTIL,

        MAXI DIR STAA,  ( store maximum value )
                 NEXT
 END-CODE


 ( Extra Problem for the Forth Assemblers! )
 ( Write a code definition and a high level definitions for the word )
 ( MAX_BYTE that takes the address of a byte array and the byte count)
 ( on the stack and leaves the maximum value in the byte array on the)
 ( stack.        MAX_BYTE  ( adr n -- max )
 ( Make sure that it works for both direct and extended page byte     )
 ( arrays. )

 NET/Mail : British Columbia Forth Board - Burnaby BC - (604)434-5886   
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