DASMx -- A microprocessor opcode disassembler

 Copyright 1996-1998 Conquest Consultants

Version 1.20, 2nd April 1998

Introduction

DASMx is  a disassembler for  a range of common  8-bit microprocessors. The
following main processor families are supported:

   o Motorola 6800 family and single chip variants;
   o Motorola 6809;
   o MOS Technology/Rockwell 6502;
   o Zilog Z80;
   o Intel 8048 family;
   o Intel 8080 family;
   o Signetics 2650.

The disassembler takes as  input a binary code/data image file (typically a
ROM image) and generates either an assembler source file or a listing file.
DASMx is  a two-pass  disassembler with automatic symbol  generation. DASMx
can  optionally  use  a symbol  file  containing  user-defined symbols  and
specifications of data areas within the source image.

DASMx includes  a powerful feature called code  threading. Using known code
entry points  (e.g. reset and interrupt  vectors) and by performing partial
emulation of  the processor, the disassembler is  able to follow known code
paths within a source binary image.

Use  of code  threading, together  with the  two-pass operation  and symbol
table management  permits readable assembly code  output from source images
that  contain   large  amounts   of  data  (which  tend   to  confuse  most
disassemblers).

DASMx  is copyright software.  This version  (1.20) may be  distributed and
used freely  provided that all  files are included in  the distribution, no
files are  modified (including the distribution zip  file) and no charge is
made  beyond   that  reasonable  to  cover   copying  (say  5  UK  pounds).

Historical note : The previous release  of DASMx,  version 1.10, superseded
the Motorola 680x disassembler,  dasm6800 (last released as version 1.00 on
25 th  January 1997.)  The  change  of name  reflected  the  wide range  of
processors now covered.

Summarising, the key features of DASMx are:

   o Disassembly of object code images for the following microprocessors:
                  + Motorola 6800/6802/6808;
                  + Motorola 6801/6803;
                  + Motorola 6809;
                  + MOS Technology/Rockwell 6502;
                  + Zilog Z80;
                  + Intel 8080/8085;
                  + Intel 8048;
                  + Signetics 2650.
   o Two pass operation, with automatic symbol generation for jump, call
     and data target addresses;
   o Code threading (used to automatically differentiate code from data);
   o Control file containing user defined symbols, specifications of data
     areas and code entry points;
   o Generation of full listing or assembler output file;
   o Runs from the command line under Windows 95 or Windows NT.


Version history

  Version         Date        Comments

    0.90     28th July 1996   First public release (as dasm6800): with
                              support for 6800/6802/6808 only.

    1.00      25th January    Second release (as dasm6800): 6801/6803 and
                  1997        6809 support added; other improvements in
                              performance and listing output.

    1.10     16th July 1997   Third release (now renamed DASMx): 6502,
                              Z80 and 8048 processor support added; minor
                              improvements and bug fixes.

    1.20     2nd April 1998   8080, 8085 and 2650 processor support
                              added; improvements and bug fixes.


The changes from version 1.10 are:

   o Disassembly of Intel 8080 and 8085 added (in addition to existing
     support for 8080 provided by Z80 disassembly);
   o Disassembly of Signetics 2650 added;
   o New symbol file command to skip areas of source image;
   o Origin can now be specified in symbol file;
   o New command line option to specify a single code entry point for
     threading;
   o New command line option to list all processors supported;
   o Fix to incorrect disassembly of 6801/6803 subd instruction (opcode
     0x93);
   o Bug fixes and other minor changes.

The changes between versions 1.00 and 1.10 were:

   o All references to "dasm6800" replaced by "DASMx";
   o Disassembly of 6502 added;
   o Disassembly of Z80 added;
   o Disassembly of 8048 added;
   o Minor bug fix for code threading of 6801/6803 direct branch
     instructions;
   o Minor changes to listing output;
   o Bug fixes and other minor improvements.

The changes between versions 0.90 and 1.00 were:

   o Disassembly of 6801/6803 added;
   o Disassembly of 6809 added;
   o Define byte pseudo-op now generates full listing;
   o Two new commands supported in symbol file: cpu (to select processor
     type) and addrtab (to define a table of addresses, each of which
     points to data);
   o New command line switch to select processor type;
   o Performance improvement to pass 1;
   o Minor changes to listing output;
   o Bug fixes and other minor improvements.


Copyright

DASMx and all associated  documentation are copyright Conquest Consultants.


Disclaimer

DASMx comes without any  express or implied warranty. You use this software
at your  own risk.  Conquest Consultants have  no obligation to  support or
upgrade this software. Conquest  Consultants cannot be held responsible for
any act of copyright infringement or other violation of applicable law that
results from use of this disassembler software.


Distribution

DASMx  is copyright software.  This version  (1.20) may be  distributed and
used freely  provided that all  files are included in  the distribution, no
files (including  the distribution zip file) are  modified and no charge is
made beyond  that reasonable to  cover copying (say 5  UK pounds). Conquest
Consultants reserve the right  to alter the free distribution and use terms
for  any future  versions or  derivatives of  DASMx  that may  be produced.

DASMx version 1.20 is distributed as file dasmx120.zip in the /msdos/disasm
section  of the  Simtel and  Simtel.net archives.  Provided that  the above
distribution terms  are adhered to, this  file may be freely  copied to and
mirrored at other ftp and WWW sites.


Operation

Before describing the operation  of DASMx in detail, here is an overview of
how the disassembler will be typically used in practice.

First, you  must obtain a file  containing a binary image  of the code/data
that you wish to disassemble. Typically, this will be from one or more ROMs
or  EPROMs  that  have  been  read  using  a  PROM  programmer.  Some  PROM
programmers output  data in a  form of ASCII hexadecimal  format (Intel and
Motorola are two common  formats). If that is the case, then you must use a
conversion utility  to generate a raw  binary image. A good  check that you
have  a correct  binary image  of a  complete ROM  is that the  file length
(shown by a DIR  command) will be a power of two and will correspond to the
length of  the ROM.  For example, the  file size of  a complete  image of a
27256 EPROM will be 32,768 bytes.

Assuming at this stage that you do not know which areas of the binary image
are  code and  which are  data, it  is sensible  to use the  code threading
feature. For  code threading  to work, you  must provide at  least one code
entry point. This requires code, vector or vectab entries in a symbol file.
For example, if you are disassembling a ROM image from the uppermost region
of the 6800 microprocessor  address space, then four vector entries for the
standard interrupt and reset vectors will be all that is initially required
to provide the necessary entry points. You can also improve the readability
of  the disassembled  output  by defining  symbols for  all  known hardware
addresses (e.g. PIA registers and other ports).

Try modifying  the supplied example symbol file ( ebcgame.sym) to suit your
application. It  is important that the  correct processor type is specified
using a  cpu directive in the symbol file (or  by command line switch). The
disassembler will  not make  much sense of  Z80 code if it  thinks that the
processor is a 6502!

Run  the disassembler  with code  threading. This  will identify  all known
areas of  code. Data and unknown  areas will be listed  as byte data rather
than  disassembled into  instruction mnemonics.  Due to limitations  of the
code threading  process (see below)  not all code areas  may be identified.
Any additional  code entry points or address vector  tables can be added to
the symbol file. Similarly,  areas of byte, word or string data that can be
identified from examination of the disassembly listing can also be recorded
in the symbol file.

Using a repeated "disassemble, inspect listing, update symbol file" cycle a
comprehensive  disassembly  of an  image  can  be built  up quite  quickly.

Finally, if you are satisfied that you have identified all main data areas,
try disassembling  without code threading. This will  help pick up areas of
code that may have  been missed by the code threading and subsequent manual
investigation process.


Platform

DASMx  is a  Win32  console application.  This means  that  it is  a 32-bit
application that  requires Windows 95 or Windows  NT to run. Typically, you
will run the disassembler from a DOS box command line.


Command line options

DASMx has the following command line options:

 -a           generate  assembler output  (default is  to generate  a full
              listing file);

 -cTYPE       set  the CPU processor type  overrides any cpu statement in
              the  symbol file, where TYPE is one of the types reported by
              the   l option  (6800,  6809, 6502,  Z80 etc.)  (default is
              6800);

 -eNNNN       specify code entry point NNNN for threading;

 -l           list all processors supported and exit;

 -oNNNN       set  the origin, or start address to NNNN (default is top of
              address   space  less  the  length  of  the  source  image);

 -t           perform code threading (requires presence of a symbol file);

 -v           display version information and exit.

When  specifying addresses,  the number  NNNN  should be specified  using C
language  conventions (i.e.  default is  decimal, prefix  with 0x  for hex,
prefix with 0 for octal).


Input files

The  primary  input  file  is  a  binary  image  of  the  code/data  to  be
disassembled. This  must be  code for one of  the supported microprocessors
(or other  manufacturer equivalent.) DASMx  will produce meaningless output
for any other type of processor.

DASMx assumes a file extension of ".bin" unless otherwise specified for the
binary image file.

DASMx looks  for a symbol file  of the same base  name as the source binary
file, but with a  ".sym" file extension. If a symbol file is found, it will
be  used.  Provision  of  a symbol  file  is  optional,  except where  code
threading is used (where  a symbol file must be used to define at least one
code entry point).


Symbol file syntax

The symbol file is  a plain text file that may be created/modified with any
text  editor.  The  file  contains  lines  that  fall  into  one  of  three
categories:

   o comment lines;
   o command lines;
   o blank lines.

Comment lines  are denoted by ; as  the first non-whitespace character on
the  line.  Command  lines  start  with  one  of  the  specified  keywords.
Parameters  follow the  command  keyword, separated  by spaces  or  tabs. A
comment  may  be  added to  the  end  of a  command,  preceded  by the  ;
character. Blank lines are ignored.

Number value parameters may be given in decimal (the default), octal or hex
using  standard   C  language   conventions  (e.g.  0x   prefix  for  hex).

Valid command keywords and their meaning are summarised in the table below.

 Command      Function/syntax

 cpu          Specify the processor type.
              Syntax: cpu 2650 | 6502 | 6800 | 6801 | 6802 | 6803 | 6808 |
              6809 | 8048 | 8080 | 8085 | Z80

 org          Define the start address for the first byte of the code/data
              image. Note that only one org statement should be present in
              a symbol file.
              Syntax: org <address>

 symbol       Define a symbol corresponding to a value (usually an
              address).
              Syntax: symbol <value> <name>

 vector       Define a location that contains a word pointing to a code
              entry (for example, the reset entry point).
              Syntax: vector <address> <vector name> [<destination name>]

 vectab       Define a table of vectors (i.e. a jump table) of length
              <count>. Each vector will be used as a code entry point if
              threading is used.
              Syntax: vectab <address> <name> [<count>]

 code         Define a code entry point (for code threading).
              Syntax: code <address> [<name>]

 byte         Define a single data byte, or <count> length array of bytes.
              Syntax: byte <address> <name> [<count>]

 word         Define a single data word, or <count> length array of words.
              Syntax: word <address> <name> [<count>]

 addrtab      Define a table of addresses, which point to data, of length
              <count>.
              Syntax: addrtab <address> <name> [<count>]

 string       Define a single data character, or <count> length string of
              chars.
              Syntax: string <address> <name> [<count>]

 skip         Skip (i.e. omit from disassembly and listing) <count> length
              data bytes.
              Syntax: skip <address> <count>


Output files

By default, DASMx  generates a disassembly listing file. This is similar to
the full  listing file generated by most  assemblers. Optionally, DASMx can
be made  to produce an assembly file instead. This could  then be used as a
source  file  to  an  assembler  of  your  choice  (with  certain  provisos
concerning pseudo-ops and number formats noted later).

As an aid to  readability, DASMx inserts a comment line after all breaks in
a sequence of instructions  (e.g. after an unconditional branch or jump, or
a return from subroutine). Comment lines are also inserted between code and
data  areas. This  use  of comment  lines  breaks the  output listing  into
identifiable  sections   and  aids  manual  inspection   of  the  resultant
disassembly listing.

Note that output files  tend to be large. For example, a 32 Kbyte ROM image
will  generate  a  listing  file  of  around  half a  megabyte  in  length.

The output file is  named based upon the name of the source image file, but
with  a file  extension  of ".lst"  for the  list  file or  ".asm"  for the
assembly output file.


Code threading

Code threading is a  very powerful feature that will automatically identify
known areas  of code. It can prove particularly  useful in the early stages
of disassembly  of an  image that contains  large areas of  data. Such data
areas  would otherwise be  disassembled incorrectly  as code and  would add
many erroneous symbols to the symbol table.

Code threading  works by  performing a partial emulation  of the processor;
executing instructions  starting from one or  more known entry points. Code
threading follows  calls to  subroutines and conditional  and unconditional
branches. In  certain cases, the code threading  may fail to follow certain
code paths  (i.e. leaving valid code still  defined as data). The following
are  examples of  where the  code threader  will fail  to follow  a correct
execution path:

   o pushing an address onto the stack and then, later, performing a return
     from subroutine instruction (i.e. as a method of performing a jump);
   o performing an indexed branch instruction (e.g. using addresses taken
     from a vector table);
   o use of undocumented instruction opcodes  since threads are abandoned
     when an invalid opcode is detected;
   o self-modifying code.

Indexed  branch  instructions  are highlighted  in  the  output listing  by
automatically generated comments. These  are an indication that you need to
manually identify what the  contents of the index register will be prior to
the  branch (often  obvious   look  for  a preceding  load index  register
instruction.) Then, you can add a code or a vectab entry to the symbol file
and repeat the disassembly.

In  rare  cases, code  threading  may  incorrectly identify  data as  code:

   o a call to a subroutine that never returns (e.g. the subroutine
     discards the return address); the other side of the call containing
     data rather than code.
   o a conditional branch that is always, or never, executed (and the other
     side of the branch contains data rather than code).

Normally  this   latter  scenario   is  pretty  unlikely   and  requires  a
particularly  perverse programmer of  the original  code. However, it  is a
technique that may be  encountered on those processors which had a "better"
(i.e. fewer cycles and/or  fewer bytes) conditional jump than unconditional
jump. So,  in general, code threading  will identify guaranteed known areas
of code that may  be a subset of the overall actual code. Most of the above
problem areas  can be  dealt with by  manual inspection of  the disassembly
listing and subsequent additions to the symbol file.

A thread of execution will be abandoned for one of two reasons. If a branch
or subroutine  call is made outside the  address range corresponding to the
source  image  then  that  thread is  not  followed.  Also,  if an  invalid
instruction is  detected then the thread  terminates immediately. This will
produce  a command  line error  message identifying  the address  where the
problem occurred.  Normally this represents an  error condition that can be
corrected by the person operating the disassembler:

   o the processor type is incorrectly specified;
   o the source binary image is not real code;
   o an incorrect code entry point has been supplied;
   o so called "undocumented" instructions have been used.

In rare cases, the  original programmer may have done something that causes
the code  threader to  incorrectly identify data  as code. These  cases may
also result in invalid instruction messages.


Microprocessor specifics

The following sub-sections detail items of note relating to disassembly for
the  specific microprocessors  (and  their variants)  supported by   DASMx.


Motorola 6800/6802/6808

The  Motorola  6800, 6802  and  6808  share an  identical instruction  set.

Assembler mnemonics follow the Motorola standard definitions (see reference
[1]). Note that there  are two common styles for instructions involving the
A and B registers:

   o the A or B register name is separated by whitespace from the base
     instruction (e.g. lda b value);
   o the A or B register name is used as a suffix to the instruction
     mnemonic (e.g. ldab value).

DASMx uses  the latter style. This point also  applies to the 6801/6803 and
6809 mnemonics generated by the disassembler.


Motorola 6801/6803

The Motorola  6801 and 6803 share  an identical instruction set  that is an
object code compatible superset  of that of the base 6800. These processors
contain on-chip  timer and I/O plus an  expanded interrupt vector area over
that of the 6800. Definitions for these in a symbol file will be useful for
disassembly  of any  6801/6803  code. See  the supplied  6803 symbol  file,
ebcgame.sym , for an  example that could  be used  as a template  for other
6801/6803 disassembly.


Motorola 6809

The Motorola  6809 has an instruction  set that is compatible  with that of
the  6800 at the  assembler level (i.e.  it is  not binary  compatible, but
every 6800  instruction mnemonic  is present in the  6809 instruction set).
The 6809 also has  many additional instructions that are not present in the
6800.

With certain  provisos, if the  CPU type is set  to 6809 then  DASMx can be
used  to disassemble  code from  a Hitachi  6309 processor. That  device is
object code  compatible with the 6809,  with additional instructions. DASMx
will  not  recognise  these extra  instructions.  Consequently,  it is  not
advised   to   use   code   threading   when   disassembling   6309   code.


MOS Technology/Rockwell 6502

The MOS  Technology/Rockwell 6502 has a similar  instruction set to that of
the 6800 (but totally opcode incompatible).

A number  of 6502  variants, with expanded instruction  sets and addressing
capabilities,  have  appeared  over  the  years.   DASMx  may  be  used  to
disassemble code for these  6502 variants (such as the Rockwell 65C02), but
it  will not  cope with  their additional instructions.  Consequently, code
threading will not operate effectively on such devices.


Zilog Z80

The Zilog  Z80 (also made by  Mostek, Sharp, NEC and  other second sources)
has an  instruction set  that is binary  compatible with that  of the Intel
8080, but with many additional instructions. Although each 8080 instruction
has an  identical Z80 instruction, Zilog chose  to use a different mnemonic
style for  almost every  instruction. Consequently, Z80  assembler (even if
restricted  to the  8080 subset)  appears quite  different even  though the
resulting binary image is identical.

The  Z80  has  a  great many  (so  called)  undocumented instructions  that
(sometimes)  perform useful  functions.  DASMx  does not  currently support
these additional instructions.

Like the  6502, the  Z80 has spawned  many variants with  opcode compatible
instruction supersets. DASMx can be used on code for these devices with the
standard caveat  that any of the new  instructions will not be disassembled
as   valid   code  (and   therefore   code  threading   is  not   advised.)


Intel 8080 and 8085

The  Intel 8080  and 8085  share an  almost identical instruction  set. The
Intel  8085  is  an  enhanced version  of  the  8080,  with two  additional
instructions ( rim and  sim)  used to control  new serial in  and out pins.

When disassembling  8080 (and, with  provisos, 8085) code the  user has the
option  of generating either  Intel or  Zilog mnemonics. To  generate Intel
mnemonics, simply  specify the  CPU type to  be 8080  or  8085 as required.

Generating  Zilog Z80  style  mnemonics from  Intel 8080  code  is possible
because the 8080 has  an instruction set that is a compatible binary subset
of those of the  Z80. Simply specify the CPU type is as  Z80 and DASMx will
correctly disassemble  8080 code  into Zilog mnemonics. This  will not suit
Intel assembler die-hards, but may be preferred by those more familiar with
the Z80.

WARNING: if DASMx  is used as a Z80 disassembler on 8085 code and either of
the two  8085 specific  instructions are used ( rim and sim ) then problems
will result.  In such cases Zilog disassembly  is probably best avoided. If
you really must have Zilog mnemonics then read the following description of
how these  instructions are handled  and be prepared for  code threading to
work incorrectly.

rim is  a one byte instruction, but DASMx  will attempt to disassemble this
as  the two byte  jr nz Z80  instruction. This  will both generate  a false
label and ignore the  next byte in the 8085 opcode stream. Since that could
be  the  first byte  in  a  multi-byte opcode  it  could take  a number  of
erroneously disassembled  instructions before  synchronisation is achieved.

sim is  a one byte instruction that will be  disassembled as the first byte
of the three byte  ld hl immediate instruction. The results will be similar
to those for rim.


Intel 8048 (MCS-48(tm) family)

DASMx will disassemble opcodes for the following Intel MCS-48&trade; family
devices  (and equivalents  from second  source manufacturers):  8021, 8022,
8035, 8039, 8041, 8741,  8048, 8049 and 8748. The CPU type should be set to
8048 and the term  "8048" is used throughout this documentation to refer to
this family of devices.

The 8021  instruction set is a much reduced subset of  the full 8048 set of
instructions.

The 8022 has a  very similar instruction set to the 8021, but with slightly
more  of the  8048 instructions and  a few  new instructions to  handle the
on-chip analogue to digital converter.

The 8041/8741  has almost  the same instruction  set as the  8048, but with
just a few instructions missing.

DASMx can disassemble code  for the 8021, 8022, 8041 and 8741 variants with
the caveat  that data areas  may be disassembled as  8048 instructions that
are in fact illegal on the variant.

The  8048 jump  and call  instructions operate  on an 11-bit  address (i.e.
within a 2 Kbyte memory  bank). A memory bank select bit (controlled by the
sel mb0  and sel mb1  instructions) is  combined with the  11-bit jump/call
address to give full  12-bit addressing within the 4 Kbyte address space of
the  8048. This  presents a  problem for  the code threading  and automatic
label generation functions of DASMx since a destination address can only be
fully  calculated  if  the  last memory  bank  select  operation is  known.
Tracking the  state of the memory  bank select bit is  currently beyond the
capabilities of  DASMx. For this reason, it  is advised that code threading
be  not used  if the  size of  the 8048  source image exceeds  2 Kbytes. If
images greater  than this  are disassembled, even  with threading disabled,
some   errors  in   automatically   generated  labels   may  be   expected.


Signetics 2650

The  Signetics 2650  is a  rather oddball  processor when compared  to most
other  processors handled  by  DASMx . It  operates on  8-bit data  and can
address 32,768 bytes of memory organised in four pages of 8,192 bytes each.
It has a large  range of addressing modes, made possible by the use of bits
encoded in  the second  byte of two  and three byte instructions.  It has a
3-bit stack pointer which means that subroutines can be nested to, at most,
eight deep.


Assembler pseudo operations

Assembler pseudo operations (e.g.  that to define a data word) are not in a
standard style that matches the chosen processor. The pseudo-ops are common
across all processor disassembly  output. In general, the pseudo-ops follow
Intel conventions:

   o the ; character to denote a comment;
   o the : character following a label;
   o db, to define a data byte, character or string;
   o dw, to define a data word;
   o org, to specify a starting address.

If  these do  not suit  your preferred  assembler, then  use of  search and
replace  in  a  text  editor  can  probably effect  the  required  changes.


Number format

The  number  format  used  in  the  disassembled  output  follows  Motorola
conventions (just  to be perverse!)  a preceding  $ character is used to
denote  a hex  address value.  Immediate values  (again, given in  hex) are
preceded by a #  character. All numbers and addresses in the listing part
of  the  disassembly output  are  given  in hex,  although  for clarity  no
preceding $ characters are used.

Numbers  in the  operand field  of a  disassembled instruction  are usually
given in hex. Small positive or negative offsets in 6809 index instructions
are given as a signed decimal number.


Future enhancements

Whilst  there is  no guarantee  that future  versions of  this disassembler
software will be released, some or all of the following areas are likely to
receive attention in any future version:

   o fixing any errors discovered in the instruction mnemonics or
     disassembly of an opcode to its instruction;
   o rationalisation of the pseudo-ops and number format such that the
     assembler output can be fed directly into at least one common
     assembler without further text editing;
   o improved code threading (through use of a more complete emulation of
     the processor);
   o improved symbol table output in listing file;
   o specifying comments in the symbol file for inclusion in the output
     files;
   o additional memory map output in listing file;
   o inclusion of clock cycle count information in listing file;
   o better support for 8048 code greater than 2 Kbytes and for 8048
     variants;
   o support for other 8-bit microprocessors (e.g. Intel 8051);
   o support for variants of the currently supported processors (e.g.
     Hitachi 6309, Rockwell 65C02);
   o disassembly of commonly known "undocumented" instructions.

Fixing actual  disassembly errors  (if any are discovered)  will be treated
with priority.

Note  that it  is not  currently intended  to support platforms  other than
Windows 95  or NT. In particular, there will be  no 16-bit versions for DOS
or  any other  16-bit  operating systems.  If  the demand  exists, a  Linux
version may be produced.


Contacting the author

Feedback  to  Conquest  Consultants  may be  made  via  pclare@bigfoot.com.


References

The  following  publications  were   referred  to  in  the  course  of  the
development of DASMx . This may also be considered to be a useful reference
list  for anyone  programming  these processors  at assembler  level and/or
inspecting the output of DASMx.

  [1]   M6800 Microprocessor Applications Manual, Motorola Semiconductor
        Products Inc., First Edition, 1975.

  [2]   Hitachi Microcomputer Databook 8-bit HD6800 & 16-bit HD68000,
        Hitachi Ltd., March 1983.

  [3]   Programming the 6502, Rodnay Zaks, Sybex, ISBN 0-89588-046-6,
        Third Edition, 1980.

  [4]   6502 Assembly Language Programming, Lance A.Leventhal,
        Osborne/McGraw-Hill, ISBN 0-931988-27-6, 1979.

  [5]   6502 Assembly Language Programming, Second Edition, Lance
        A.Leventhal, Osborne/McGraw-Hill, ISBN 0-07-881216-X, 1986.

  [6]   R650X and R651X Microprocessors (CPU), Rockwell, 29000D39, Data
        Sheet D39, Revision 6, February 1984.

  [7]   MCS6500 Microcomputer Family Programming Manual, MOS Technology
        Inc., Second Edition, January 1976.

  [8]   1984 Data Book, Semiconductor Products Division, Rockwell
        International, March 1984.

  [9]   TLCS-Z80 System Manual, Toshiba, 4419 84-05(CK), June 1984.

 [10]   Microcomputer Components Databook, Mostek, MK79778, July 1979.

 [11]   Z80-Assembly Language Programming Manual, Zilog, 03-0002-01, Rev
        B, April 1980.

 [12]   MCS-48&trade; Users Manual, Intel, 9800270D, July 1978.

 [13]   48-Series Microprocessors Handbook, National Semiconductor, 1980.

 [14]   Component Data Catalog, Intel, 1980.

 [15]   An Introduction to Microcomputers: Volume 1, Basic Concepts,
        Second Edition, Adam Osborne, Osborne/McGraw-Hill,
        ISBN 0-931988-34-9, 1980.

 [16]   Osborne 4 & 8-Bit Microprocessor Handbook, Adam Osborne & Gerry
        Kane, Osborne/McGraw-Hill, ISBN 0-931988-42-X, 1980.

 [17]   2650A/2650A-1 Data Sheet, Signetics.


