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                          X68000: version for use on IBM PC



       PREFACE



       This document describes the use of X68K and E68K on  the  IBM  Personal
       Computer.  X68K is a cross-assembler based on the assembler provided by
       Motorola, and  E68K  is  a  program which emulates the instructions and
       architecture of the Motorola MC68000 chip.























































                          X68000: version for use on IBM PC



       1  X68K Motorola M68000 cross assembler


       The X68K assembler is based upon the assembler  provided  by  Motorola.
       It will  assemble  all  the valid instruction mnemonics as described in
       Motorola publications, and accepts some of the directives.  The current
       release of X68K will only generate absolute code and does  not  include
       facilities for structured assembly.  Of the directives supported by the
       Motorola assembler the following are accepted by X68K.

            DC, DCB, DS, END, ENDC, ENDM, EQU, FAIL, FORMAT, NOFORMAT,
            IFxx, INCLUDE, LIST, NOLIST, MACRO, MEXIT, PAGE, REG, SET,
            SPC, TTL.

            OPT (A, BRL, BRS, CEX, NOCEX, CL, NOCL, CRE, FRL, FRS, MC,
                 NOMC, MD, NOMD, MEX, NOMEX, PCO, NOPCO)

       The usage of all the above  is  documented  in  the  official  Motorola
       assembler manual.  However, there are some minor points to be made:

         i) By default X68K generates no  symbol  table  information  in
            the  listing  file.  OPT  CRE  causes symbol table and cross
            reference  information  to  be  displayed,  instead  of just
            cross reference information.

        ii) OPT NOCL is  used  to  stop  conditional  "IFxx"  directives
            being  displayed in the listing file. This has been extended
            to  include  instructions that are skipped as a result if an
            "IFxx" directive being false.

       iii) The text string that  follows  the "TTL" directive  MUST  be
            enclosed in single quotes.    Only  the last "TTL" directive
            will be used as  a title in the listing file. Similarly  the
            pathname ised in the "INLCUDE" directive must be enclosed in
            single quotes.

        iv) The  "END"  directive must have a label, as this defines the
            start address of the assembled program.

       If OPT MEX is used and a listing file produced there may be more  lines
       in the  listing file than there were in the original source file.  This
       will be due to macro expansions.  In order to make it easier to  relate
       a listing file to the original source file, X68K will place two sets of
       line numbers in the listing file if macros have been called.  The first
       column of  line numbers is used by X68K for cross referencing purposes.
       The second set of line numbers relate to source lines in  the  original
       file, and are displayed in parenthesis.

       Any error messages displayed on the screen during assembly will  be  of
       the form:

             Line NN, error message                OR
             Line NN.XX, error message

       In both cases the NN part refers to  a  line  number  in  the  original
       source file being assembled.  The XX part will be used when an error is
       detected in a macro expansion which started at line NN.


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                          X68000: version for use on IBM PC



       To call X68K the command is:

              X68K filename
        or
              X68K filename/L      (if a listing file is wanted)

        where the full name of the file is filename.X68

       If the assembly is error-free, a binary output file  will  be  produced
       with the  name  "filename.BIN".  The assembler was written primarily to
       be used with E68K the Motorola M68000 system emulator.  Because of this
       the following points should be noted.

       The assembler initializes the program counter "PC" to zero  before  any
       code is  produced  and  will  only  allow PC to be altered to addresses
       higher than PC through the use of ORG directives.  This will stop users
       from causing code overlays.  However, all user programs  will  normally
       have as  their first non-comment statement an ORG $400 directive.  This
       is because the 68000 holds exception vectors from $0 to $3FF.   The  PC
       is set  to  zero  initially  to  allow  users  to  use ORG to place the
       addresses of exception handlers in the vector table  before  generating
       code.

       Expressions within the assembler are broken into three  types,  string,
       arithmetic and  logical.   All  non-string  expressions are taken to be
       arithmetic expressions unless they  contain  any  of:   (!,&,<<,>>)  or
       non-base-ten numbers.  An expression may contain a string e.g.  'A'!$80
       results in  logical  hex  C1 where 65+128 results in arithmetic hex C1.
       This has the effect that statements such as:

                                    AND.B  #$FF,D0

       are legal since $FF is an eight bit quantity.  But statements such  as:

                                    AND.B  #255,D0

       are not legal since the arithmetic range for byte operations is -128 to
       127.

       Any forward reference to a label defined by a SET directive will  cause
       the value of the last SET directive in the program to be returned.

       For information on M68000 instructions and  assembler  conventions  see
       the following books:

         M68000 16/32-BIT MICROPROCESSOR PROGRAMMERS REFERENCE MANUAL,
         ISBN 0-13-566795-X (Prentice-Hall)

         M68000 RESIDENT STRUCTURED ASSEMBLER REFERENCE MANUAL







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                          X68000: version for use on IBM PC



       2  E68K Motorola M68000 system emulator


       E68K is  a  program which emulates the instructions and architecture of
       the M68000.  The emulator supports an addressing range of 10240 kbytes,
       memory being allocated when first written to.  To call E68K the command
       is

            E68K [filename]

       where the full name of the input file is filename.BIN.  The binary file
       may be one produced by X68K or  a  memory  dump  by  E68K.   Memory  is
       allocated in 1KB chunks from addr 0.  The user need not use memory in a
       contiguous fashion.   If  the user tries to exceed the memory available
       on the computer, an error message is printed and a Bus_error  exception
       is generated.

       The emulator  initializes the vector table to zeros before any programs
       are loaded.  If, when an exception  occurs,  the  vector  is  zero  the
       emulator will  take  a  default  action.   Otherwise  normal  exception
       processing takes place.  The emulator is always in one  of  two  modes.
       It is  either  executing a program or it is processing commands.  Below
       is a list of the available commands and their meaning.


          2.1  HELP


          The HELP command will respond with the following display.

           .PC .SR .US .SS
           .D0 .D1 .D2 .D3 .D4 .D5 .D6 .D7
           .A0 .A1 .A2 .A3 .A4 .A5 .A6 .A7
           .C  .N  .V  .X  .Z

           BF - Block fill,                       GT - Go with temp brkpt.
           BM - Block move,                       HE - Help.
           BR - Set/display brkpts,               LO - Load binary file.
           BS - Block search,                     MD - Memory dump.
           DC - Data conversion,                  MM - Memory modify.
           DF - Display registers,                MS - Memory set.
           DU - Dump memory to file,              NOBR - Remove brkpts.
           GD - Go direct,                        TR - Trace program.
           GO - Execute program with brkpts,      QUIT - Return to MS-DOS.

           For more detailed information type: HE command-name
                                               HE INFO
                                               HE EXCEPTIONS
                                               HE TRAP#15







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          The first three lines which specify register names indicate that the
          contents of any register can be  displayed  by  entering  .Rn  as  a
          command.  The  contents  of  registers  can  be altered in a similar
          fashion e.g.  entering .PC $1000 assigns the value hex 1000  to  PC.
          This feature  is  also  available for the status register flags e.g.
          .Z 1 would set the ZERO flag to true.  The  emulator  supports  full
          expression   processing  using  the  same  operators  and   operator
          priorities as the  assembler.   The  only  difference  is  that  the
          default base  of  the  emulator  is hex, and decimal numbers must be
          preceeded by a  "^".   The  register  names  may  also  be  used  in
          expressions e.g.  .PC .PC+2 increments PC by 2.

          The remainder of the help display lists  the  valid  command  names,
          which are explained below.


          2.2  BF - Block fill


           Format: BF <addr_1> <addr_2> <data>

          The BF  command is used to fill a block of memory starting at ADDR_1
          and ending at ADDR_2 with DATA.  All arguments to this  command  are
          integers.  The command uses word operations only.


          2.3  BM - Block move


           Format: BM <addr_1> <addr_2> <addr_3>

          The BM  command is used to move a block of memory starting at ADDR_1
          and ending at ADDR_2 to a new  location  staring  at  ADDR_3.   This
          operation is  byte  oriented.   The  two  areas  of  memory must not
          overlap.





















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                          X68000: version for use on IBM PC



          2.4  BR - Set and display breakpoints


           Format: BR <brkpt_1> ... <brkpt_7> -<count>

          The BR command allows a user to  insert  or  remove  breakpoints  in
          memory.  Associated  with  each  breakpoint  is a count.  This count
          specifies how many times the breakpointed location can be referenced
          before a break is taken.  If no count is specified the default value
          is zero.  Upto seven breakpoints can be inserted with the BR command
          in one go if a count is specified, eight otherwise.  If BR  is  used
          with no  options  the  existing  breakpoint  table is printed.  Upto
          sixteen breakpoints can be in force  at  once.   Breakpoints  should
          only be  inserted in the first word of an instruction.  Placing them
          in the  middle  of  instructions  will  probably  cause  an  illegal
          instruction   exception  when  the  instruction  is  executed.   The
          breakpoint count is reset when any of  the  following  commands  are
          executed "GO",  "GT",  "TR n".  Breakpoints for the "TR" command are
          ignored when N is one.


          2.5  BS - Block search


           Format: BS <addr_1> <addr_2> 'string'
                   BS <addr_1> <addr_2> <data> [<mask>] [-B] [-W] [-L]

          The BS command is used to search  a  block  of  memory  starting  at
          ADDR_1  and  ending  at  ADDR_2.   The  first  format  searches  for
          character strings.  The second  searches  for  DATA.   The  location
          being tested  may be optionally anded with MASK before testing.  The
          block search for non-strings may be byte, word or  long_word  based.
          The default  is byte.  If any matches are found the start address of
          the match is printed.


          2.6  DC - Data conversion


           Format: DC expression

          This command evaluates an expression and prints it in hex,  decimal,
          octal and  binary.   As  with  the  assembler,  expressions must not
          contain embedded blanks.












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                          X68000: version for use on IBM PC



          2.7  DF - Display formatted registers


          The DF command displays all the  current  register  values  and  the
          various elements  of  the  condition  code register separately.  The
          instruction pointed  to  by  the  current  value  of  PC   is   also
          disassembled and displayed.


          2.8  DU - Dump memory and registers to file


           Format: DU <addr_1> <addr_2> dumpfilename

          The DU command dumps a block of memory starting at ADDR_1 and ending
          at ADDR_2  to  a disk file specified by dumpfilename.  The full name
          of the file produced will be dumpfilename.BIN.  The current register
          values are also dumped.  The dumping is by word as is  the  loading.
          See LO.


          2.9  GO - Execute program


           Format: GO <addr>

          The GO  command  causes  execution  to  begin  at address ADDR.  The
          program will execute  until  a  trap,  exception  or  breakpoint  is
          reached.


          2.10  GD - Go direct (execute program without breakpoints)


           Format: GD <addr>

          The GD  command  causes  execution  to  begin  at address ADDR.  The
          program will  execute  until  a  trap  or  exception   is   reached.
          Breakpoints are ignored.

















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                          X68000: version for use on IBM PC



          2.11  GT - Execute program with temporary breakpoint


           Format: GT <addr>

          The GT  command  inserts  a temporary breakpoint at address ADDR and
          then begins execution at  the  address  in  PC.   The  program  will
          execute until  a  trap, exception or any breakpoint is reached.  The
          temporary breakpoint is removed when execution terminates.


          2.12  LO - Load binary file


           Format: LO filename

          This command loads a file specified by filename  into  memory.   The
          full name  of  the  file must be filename.BIN, and will either be an
          E68K DUmp file or one produced by X68K.  The loading is done by word
          not byte.  If the binary file is an E68K Dump file  then  the  saved
          register contents will replace the current settings.


          2.13  MD - Memory dump


           Format: MD <addr> <count> [-DI]

          The MD  command  dumps  COUNT bytes of memory (or disassembles COUNT
          instructions if "-DI" is used) starting at address ADDR.   Once  the
          first section  has  been dumped entering carriage returns will cause
          the MD command to repeat with the next section.  The  default  value
          of COUNT is sixteen.  To stop the command enter any character before
          the carriage return.






















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                          X68000: version for use on IBM PC



          2.14  MM - Memory modify


           Format:

                MM <addr> [-B] [-W] [-L] [-O] [-E] [-HEX] [-OCT] [-DEC] [-BIN]

          The MM  command is used to display and change memory locations.  The
          options determine the operation size and type.  The defaults are  -B
          and -HEX.   -O  selects  odd bytes while -E selects only even bytes.
          The other options -B,-W and -L are obvious.  The MM  command  starts
          at address  ADDR  and  displays  it's  contents.   The user may then
          specify new data for  the  location.   The  new  data  (if  any)  is
          followed by  a  symbol  which  determines  the  next  location to be
          displayed.  An "^" means step backwards  to  the  previous  location
          while "="  means  don't move.  The default is to step forward to the
          next memory location.  Specifying a "."  terminates the MM  command.


          2.15  MS - Memory set


           Format: MS <addr> 'string'
                   MS <addr> n1 n2 ... n7

          This command  enables  the  user to set memory locations starting at
          ADDR to the values contained in the arguments.  Successive bytes are
          used until the data is exhausted.  The data may be a string value or
          numbers no greater than a 32  bit  integer.   'FRED'  would  take  4
          bytes, and $123 would take 2 bytes.


          2.16  NOBR - Remove breakpoint


           Format: NOBR <brkpt_1> ... <brkpt_8>

          The NOBR  command  simply  removes  the breakpoints specified by the
          breakpoint address arguments (BRKPT_n) from the  table.   NOBR  also
          prints the remaining breakpoint table.
















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                          X68000: version for use on IBM PC



          2.17  TR - Trace program execution


           Format: TR <count>

          The TR  command causes COUNT instructions to be executed starting at
          the current value of PC.  The program will execute until  the  count
          expires or  a trap, exception or breakpoint is reached.  After COUNT
          instructions have completed the registers are printed  and  a  trace
          prompt will appear.  Typing a newline causes the next instruction to
          be executed  and  the  registers  are dumped again.  Since the trace
          facility does not use the M68000 Trace_mode facility exceptions  may
          also be  traced.   The default value of COUNT is 1.  Breakpoints are
          only in effect when the value of COUNT is greater than one.


          2.18  I/O and other facilities


          The emulator provides a mechanism to allow users to perform  i/o  on
          numbers and  characters.   This  is  achieved  by  using  a TRAP #15
          instruction.  Should a user alter the default vector for TRAP #15 to
          a non-zero  value  this  feature  will  cease  to  work  and  normal
          exception processing will take place for this instruction.  The task
          number is in D0.B.

          See E68K : HELP TRAP#15 for information on the functions available.

       General

       The emulator has a built in disassembler which is available through the
       MD and DF commands.  Should it encounter an illegal instruction pattern
       it will be disassembled as a DC.W $nnnn statement.

       A read in an unallocated area of memory causes zeros to be returned  as
       the result.   To  keep the scheme consistent, newly allocated memory is
       always initialized to zero.

       It is possible for a user to write  an  assembler  program  which  when
       executed enters  an infinite loop.  Pressing the ESC key during program
       execution will cause the emulator to return to command mode.





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