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DR  6502    AER 201S Engineering Design 6502 Execution Simulator
    ====================================================================

    Supplementary Notes                                   By: M.J.Malone
    
			 Quick/Kick Start
			 ================
    
    Use of the Simulator
    ====================
    
   Some  of  the  dos and don'ts and the reasons for them in using
    the DR6502 program will be given first.

  1) DO put all of DR6502 in on one drive and execute it from that
     drive.   It saves hassles later since it is easier to default
     to the current drive on all DR6502 files.

  2) DO put your .bin file to be simulated  on  that  same  drive,
     same reason.
    
  3)  Try  not  to  use  pathnames  with  DR6502.  DR6502 does not
      recognize pathnames.

4) DON'T expect to see any actual input or output when using

     DR6502 without the hardware simulator card.  Without the card
     DR6502 is a software simulator only that is incapable of real
     input/output   though  such  operations  can  and  should  be
     simulated through user intervention.

5) DON'T assume there is an error in DR6502 just because your

     program  did  not  work as expected.  Many students have used
     DR6502 in the past and it has proven to work well,  though  2
     small  bugs  were  discovered in the most recent YEAR of use.
     It is very common for students to make errors in logic or  be
     mistaken   about   the   operation   of   flags  for  certain
     instructions.   If  a  genuine  error  is  encountered,   the
     following should be provided:

a) A listing of the minimum assembly program required to

	produce the error.  IE 4-10 lines long where every line is
	required to induce the error.

b) The precise keystrokes/commands required to show the

	error.    Such  documented  errors  will  be  repaired  as
	expeditiously as possible.

Starting

    ========

1) System Requirements

1. ———————

To run DR6502, a machine must be XT or AT compatible and have

    at  least  640K  of memory.  Of that 640K at least 373K must be free
    after  all  memory  resident  programs  and  ram   disks   etc   are
    installed.   If  there  is  not enough free memory in your computer,
    then some of the memory resident programs must  be  removed  or  the
    ram disk must be downsized.

page 2

2) Code Requirements

1. ——————-

Produce a pure text file containing your assembly code. Do not

    use any text editor that encodes the file in any way.

If you are using the project computer then remember that your

    final   (target)   computer  code  must  start  with  the  following
    instructions:

.ORG $E000

	  SEI
	  LDX #$FF
	  TXS
    ;
	  LDX #$00
	  LDY #$00
    InitDelay   DEX
	  BNE InitDelay
	  DEY
	  BNE InitDelay
    ;

Your code then follows. The first three statements are used to

    initialize the microprocessor stack and these are also required when
    producing  a code for DR6502.  The next six instructions are a delay
    necessary to EVERY program used on the project computer.  These  are
    required because the project board uses a non-debounced reset switch
    circuit.  Simple debouncing would violate the rise time requirements
    of  the RST signal and more complex methods would require more chips
    on the project computer board.  A small addition to the beginning of
    every student's program was not considered a problem.

At the end of your code you must have:

.ORG $FFFC

    .WORD $E000
    .END

This sets the reset vector. When the RST (reset) line is used

    to  signal  to  processor  to  begin  executing,  the  processor  is
    'hardwired' to look in  memory  location  $FFFC  to  find  a  vector
    pointing  to  the  beginning of the user program.  DR6502 expects to
    find the reset vector in the same place so  these  three  directives
    are also required in programs to be simulated.

3) Assembling

1. ————-

Any assembler capable of converting 6502 assembly language

    statements to a binary file of 6502  machine  opcodes  and  operands
    would  be  acceptable.   The TASM (Table oriented ASseMbler) is user
    supported package  available  to  AER  201S  students.   TASM  is  a
    converter  of ASC II assembly code files to binary executable files.
    It is capable of assembling for the 6502 as well  as  several  other
    processors.   It  is  a common mistake to believe that there is some
    problem with the fact that the TASM program executes on an IBM  type
    computer but produces code for a 6502 machine.  Once again TASM is a

page 3

converter program. The machine it executes on does not determine

    what type of files it produces.  TASM could be programmed to run  on
    a  Cray  but  it  would  still  produce code for execution on a 6502
    machine.

The proper command line for assembling the program 'myfile.asm'

    in the current directory is:

tasm -65 -b -l -fff myfile.asm myfile.bin myfile.lst

Note on Options: -65 : Assemble for the 6502

	       -b  :  Binary file output
	       -l  :  List the symbol table
	       -fff:  Fill unassigned spaces of the EPROM with $FF

This produces a binary file named myfile.bin ready for DR6502 or the

    EPROM programmer.  The files myfile.lst can be used to look  at  any
    errors that TASM may have found.

4) Eprom Burning

1. —————

This is actually easier than simulating the code so it will be

    dealt with first.  The PC's in the lab that are equipped with  EPROM
    burners have software installed to copy .bin files onto EPROMs.  The
    EPROM burner itself is a card for the PC computers with a cable that
    leads  to  the  EPROM ZIF (Zero Insertion Force) socket module.  You
    place your EPROM in the socket  in  the  orientation  suggested  and
    press  the  locking lever.  Place the disk with your software in the
    floppy drive and type 'EPROM'.
   The  EPROM  burner  menu has several options.  You should check
    that the EPROM type and programming  voltage  match  the  EPROM  you
    have.   Load  the file from the disk into the EPROM program's buffer
    memory starting at address  0000.   Check  the  EPROM  is  blank  by
    selecting  the  'blank  check' function from the menu.  If the EPROM
    checks out as blank, select the 'program' or 'copy' from  buffer  to
    EPROM' function to program the EPROM.  Remove the EPROM and place it
    in the target computer.
  If you would like to change the program in the EPROM or  if  the
    EPROM  did  not check out as blank before programming then place the
    EPROM in the EPROM eraser unit.  The EPROM eraser  unit  clears  the
    program  from the EPROM using ultraviolet light on the memory gates.
    Erasing requires twenty minutes under  the  ultraviolet  light.

5) Writing an EEPROM

1. ——————-

A routine has been written utilizing the hardware simulator

    interface  card,  to  write data to an EEPROM plugged into a project
    board  RAM  socket.   EEPROMS  must  be  of  the  XL2864A  type   or
    equivalent.

page 4

Simulating a Program with DR6502

    ================================

Getting to the Status Screen

1. —————————

To simulate the program DR6502 needs the code and the memory

    configuration for the target computer.  To give this information  to
    the  simulator there are two options.  1) Run the CONFIG.EXE program
    by typing CONFIG, 2) Run DR6502.EXE by typing  DR6502  and  when  it
    asks  if  it is configured for the memory of the target type 'n' for
    no.  In this case DR6502 will call the CONFIG program automatically.
   In the CONFIG program the user will be asked for  the  type  of
    memory  elements  and their addresses.  When the EPROM is specified,
    the user will be asked for the name of the .BIN file that will be in
    the memory of the target computer.  DR6502 expects to find this .BIN
    file in the current directory.
   Once the configuration is input, CONFIG will automatically call
    DR6502.  This time since you have just finished running  the  CONFIG
    program  you  can answer that 'y' "Yes, DR6502 is configured for the
    memory of the target".  Provided you do not change the name  of  the
    binary  file  in  subsequent revisions of your software, there is no
    need to run the CONFIG program again.
   DR6502 will next ask if  this  will  be  a  hardware  simulator
    session.   To  use  DR6502  in hardware mode, the hardware simulator
    card and the simulator software (DR6502) must be present in the  PC.
    The  .BIN  and all auxiliary files must be available.  The simulator
    cable must be plugged into the 6502 socket on  the  target  and  the
    target must be supplied with power from a power supply.
   DR6502  will  read  several files for information necessary for
    its operation and then will begin reading the EPROM files.   If  the
    hardware  simulator  is being used the program will ask if the EPROM
    corresponding to the file is present or not.  If the  EPROM  is  not
    present  on  the  target,  the simulator will use the PC's memory to
    emulate it.  The simulator will also ask if there is a  symbol  file
    that  goes  with  the .BIN file (a .SYM file produced with DRSYM.EXE
    and your .LST file) to be loaded into  the  simulator.   It  is  not
    necessary  to have a symbol file but it does enhance the performance
    of certain of the simulator's functions.
   The  simulator  will  next  ask  what type of processor you are
    using.  The options are 0) - NMOS 6502, 1) Standard CMOS  65C02  and
    2)  Rockwell  CMOS  65C02.   The  differences  between each of these
    processors is the instruction set.  In the newer  revisions  of  the
    processor,  some  new instructions were added.  Choose the selection
    that corresponds to the  processor  that  will  be  in  your  target
    computer.

page 5

Interpreting the Status Screen

1. —————————–

The 'stopped' status screen will then appear and it should look

    as shown below:

1. ————————-top of screen—————————–

(Errors and Warnings Area)

    ACC=00    XREG=00   YREG=00   SP=00   PC=E001      Status Register
    						  N  V  u  B  D  I  Z  C
    						  0  0  1  0  0  1  0  0
    ====================================================================
    E000 78            SEI  (2)               Fetch Address =FFFF
    E001 Next OpCode                          Vector Address=FFFF
    	     Elapsed Cycles (millions):000000.000002
    ====================================================================

    detected by DR6502 and  warns  if  the  opcode  stream  is  becoming
    unusual.   The next area down on the screen shows the current status
    of the processor registers and the flag  register.   The  next  area
    down  on  the  screen displays information about the current program
    step.  The opcode and operands  are  shown  and  then  the  assembly
    mnemonic and the addressing mode.  If the addressing mode involves a
    memory  fetch  then  the  effective  fetch address is shown.  If the
    address mode involves vector indirection then the vector address  is
    also  shown.   The  number of machine cycles since the processor was
    reset is also shown.  Below the lowest  bar  is  the  commands  area
    where user commands are input.

    manipulate  memory  or  to  start  the processor executing in one of
    several modes:

    above)  the  user can press the 's' key to cause the processor
    to advance one machine instruction or STEP and return  to  the
    'Stopped' status screen.

    the user can press the 'g' key (for GO) to cause the processor
    to   execute   a   machine   instruction,  output  all  status
    information and continue on to the next instruction.  The  's'
    key will STOP  execution  and  return  the  simulator  to  the
    'Stopped' status screen.

    execution loop, to  speed  the  processor's  progress  through
    uninteresting  parts  of the code a limited output 'fast' mode
    is available.  By pressing the '`' key in the  stopped  status
    screen,  the  user  can  cause  the  processor  to  enter fast
    execution where the screen is cleared  and  only  the  program
    counter is displayed on the screen.  By pressing '`' again the
    user can make the processor slow to full output 'go' mode.

    slows execution incredibly, a second fast  mode  was  devised.
    Often  the  user  knows exactly to what point in the code they
    would like the processor to run.  A 'breakpoint' could be used
    to halt the processor at that point and the user would need no
    screen output until that time.  As a result when the user  has
    selected  a  breakpoint  and  enters  '`'  'Go Fast' mode, the
    processor will clear the screen and enter a completely  silent
    'Really Fast' mode.

    'Go' and 'Go fast' and nearly another  order  of  magnitude  between
    that  and  'Go  Really Fast'.  The following are SOME of the options
    are available in the stopped menu.

  memory   as  a  breakpoint  for  execution.   If  the  processor
  encounters this  memory  location  any  time  during  execution,
  either  as a program location or a data access, execution in the
  'go' and 'go really fast' will stop and the full stopped  status
  screen is displayed.

  the 6502 registers including the  flags,  the  processor  status
  register and the program counter.

  data space memory so that variables or arrays can be viewed.

  into memory.

  bytes)  of  code  and displays several lines on the screen.  The
  user can then edit the code with a number of sub-options in  the
  'P'  program option.  Changes made to the code are not permanent
  unless the 's'ave sub-option is selected before the 'q'uit.

  the main output screen the contents of a memory location that is
  an important variable to the program.

    =======
   The previous explanations tried to address some of  the  common
    concerns  when  students  approach  producing  a  piece  of  project
    software for AER201S.  Complete information can only  be  gained  by
    consulting:

    a student is completely familiar with the process of moving  a  code
    from  concept  to testing and the implementation, the faster it will
    go when  design  iterations  become  necessary.   Design  iterations
    result when software never works at all on the first five tries, and
    doesn't work  completely  right  until  the  twentieth  or  fiftieth
    revision.