EDITING THE CP/M OPERATING SYSTEM

                            File: SYSTEM.TXT

                         By Walter E. Pfiester
                           1 Skadden Terrace
                          Tully, N. Y.  13159

INTRODUCTION

     Editing, changing and operating on your CP/M operating system can
be a real hassle using "DDT.COM" or "XMAN.COM".  These machine code
editors work directly on the system tracks.  It is much easier to work
on these tracks if they are saved as a file first.  This article will
detail how to save the operating system tracks as a file and later,
after editing or changing this file, placing this file back on the disk
in the proper location for use as your new version of CP/M.


SAVING THE OPERATING SYSTEM AS A FILE

     You will have to have "MOVCPM.COM" and "SYSGEN.COM" on the disk you
want to operate on.  In addition, I find it useful to have "SD.COM" (or
the enhanced version, "S.COM", "STAT.COM", and "EDFILE.COM" on the same
disk.  The first two files are used to measure the size of the files.
The later file is a machine code editor, in the public domain used to
dump and edit, full screen, any file using HEX formats OR ASCII codes.
It is not the intent of this article to delve in to the use of
"EDFILE.COM".  That can be best handled by downloading the "EDFILE.DOC"
file from your RCP/M library.

     The first thing that you must do is to measure the size, in
hexadecimal pages of memory, your operating system.  The easiest way to
do that is to type:

     A>movcpm 63 *

     For our purposes here we want to find out how many pages of memory
are required for a 63K CP/M system.  If you are using a 64K system then
type movcpm 64 *.  For this article I will use a 63K CP/M system.  As a
result of the command above, What results is as follows:

     CONSTRUCTING 63k CP/M vers 2.2
     READY FOR "SYSGEN" OR
     "SAVE 34 CPM63.COM"
      |
      +-------> This is the number we want!

     The 63 above designates the operating system size.  If you are
going to change the size of the system for later editing, recompiling or
whatever, type the size in place of 64, ie MOVCPM 55 *.


     The important thing here is to right down the number after the word
SAVE.  What MOVCPM has done for us is automatically calculate the amount
of memory required to save the CP/M image as a file.  You are done using
"MOVCPM.COM".

     Now type "SYSGEN".  In response to the question SOURCE, type a
<CR>.  When prompted as to the destination, type another <CR>.  Your
entire CP/M operating system is now in RAM, starting at 100h.  To save
this image as a file type "SAVE 34 CPM63.NEW".  34 is the number of
hexadecimal pages that you came up with above with MOVCPM.COM above.
CPM63.NEW is the file name given to save the system image as.  It could
just as easily be named anything!  It should also be noted at this time
that the operating system saved has ZCPR on it (Micro Cornucopia's
version) and it was created using instructions on their disk K22.

EDITING AND USING THE NEW (SYSTEM) FILE

     Now the file "CPM63.SYS" can be edited, changed, whatever.  I
routinely use "EDFILE" to edit machine code.  It is a full screen editor
that can be used in both the ASCII and Hex field.  Besides which, it is
one of the best FREE, public domain pieces of software!

USING EDFILE

     As an example in using this powerful tool, I will change the logon
message on cold boot to something more meaningful than:

       KAYPRO II 63k CP/M vers.  2.2

        to

       63K ZCPR-2 9/20/84
       882- 2.2

     In addition I will show you how to edit the operating system to
autoload a file on cold boot.


     The file we'll be editing is CPM63.NEW created above.  To edit
using EDFILE, type the following: "EDFILE CPM63.NEW" What will result is
as shown below:


A0>EDFILE B:CPM63.SYS

Vers: 01-10-84; by: J.C.Kaltwasser & M.J.Mosko, K3RL
File: B:CPM63.SYS Record: 00000 (0000H) LOF: 00068 (0044H)

       00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F    0123456789ABCDEF
       -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --    ----------------
0000 - C3 3E 02 43 4F 50 59 52 49 47 48 54 20 28 43 29   >C>.COPYRIGHT (C)<
0010 - 20 31 39 37 38 2C 20 44 49 47 49 54 41 4C 20 52   > 1978, DIGITAL R<
0020 - 45 53 45 41 52 43 48 20 50 6F 72 74 69 6F 6E 73   >ESEARCH Portions<
0030 - 20 28 43 29 20 31 39 38 32 2C 20 4E 4C 53 6F 26   > (C) 1982, NLSo&<
0040 - 00 29 29 29 29 29 29 29 C9 0E 01 CD 05 00 FE 61   >.)))))))I..M..~a<
0050 - D8 FE 7B D0 E6 5F C9 5F 0E 02 CD 05 00 C9 3E 0D   >X~{Pf_I_..M..I>.<
0060 - CD 57 01 3E 0A CD 57 01 C9 E5 CD 5E 01 E1 7E B7   >MW.>.MW.IeM^.a~7<
0070 - C8 E5 CD 57 01 E1 23 C3 6E 01 4F 2A 01 00 11 18   >HeMW.a#Cn.O*....<
?Search String = \KAYPRO II\

     At the prompt above, type an "S".  EDFILE will ask you for the
string to search on.  What we are doing, is searching for an ASCII
string (EDFILE can also search for a HEX string).  Reply with a
backslash "\" and the string itself followed by another backslash,  as
shown above.  Edfile will then locate the string as shown below at
address 1EE0.  This is the beginning of the log on message we are going
to change.

File: B:CPM63.SYS Record: 00061 (003DH) LOF: 00068 (0044H)

       00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F    0123456789ABCDEF
       -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --    ----------------
1E80 - C3 48 FA C3 99 FA C3 F3 FA C3 09 FB C3 2F FB C3   >CHzC.zCszC.{C/{C<
1E90 - 48 FB C3 43 FB C3 3E FB C3 7C FB C3 80 FB C3 84   >H{CC{C>{C|{C.{C.<
1EA0 - FB C3 88 FB C3 8C FB C3 90 FB C3 98 FB C3 65 FB   >{C.{C.{C.{C.{Ce{<
1EB0 - C3 A8 FB 81 00 0B 0A 08 0C 30 31 32 33 34 35 36   >C({......0123456<
1EC0 - 37 38 39 2D 2C 0D 2E 05 CD 78 FB AF 32 04 00 3A   >789-,...Mx{/2..:<
1ED0 - 33 FA 32 03 00 3A 47 FA D3 00 CD CF FB 1A 0D 0A   >3z2..:GzS.MO{...<
1EE0 - 4B 41 59 50 52 4F 20 49 49 20 36 34 6B 20 43 50   >KAYPRO II 64k CP<
1EF0 - 2F 4D 20 76 65 72 73 20 32 2E 32 0D 0A 00 3E C3   >/M vers 2.2...>C<

     Type <CTRL> E.  This will place your cursor in the HEX field.  To
move about, use the arrow keys.  To change to the ASCII field, type
another <CTRL> E.  Again, the arrow keys will move you about this field.
To edit the message, type over the message already there.   Remember,
the carriage return and line feed can not be editied in the ASCII field,
they need to be added in the HEX field.  Now that you have a new log in
message, lets save it to disk.  First, type a <CTRL> W.  This will write
all your changes out to RAM and place you at EDFILE's command level.  To
write the changes to disk and return to CP/M, type a "Q" (for QUIT).
Your are done!

     You have a new file to load in place of your old CP/M operating
system.  Once you have completed changing this file, placing it back in
the correct location on disk is very easy.  Type SYSGEN CPM63.SYS <cr>.
The prompt will ask you for the drive to place the system image to.
Type A (or B or whatever drive you want it to go to).

     A>SYSGEN CPM63.NEW

     KAYPRO SYSGEN VER 2.2
     DESTINATION DRIVE NAME (OR RETURN TO REBOOT)b <------TYPE THIS
     DESTINATION ON b, THEN TYPE RETURN <cr> <------------TYPE THIS

     FUNCTION COMPLETE
     DESTINATION DRIVE NAME (OR RETURN TO REBOOT) <cr> <--TYPE THIS

     That's all there is to it.  The next time you boot off the drive
you'll have your new system image on it with the new log in message.

     Lets do this again, in addition to the new log in message, have the
system autoload "S $AL".  "S" is a modified version of "SD-92" that I
have modified.  The $AL command tail will lok at all user areas, and
list the directory of all libraries.  Now lets modify the operating
system, again.

     This time, use the ASCII search again only look for the word
"COPYRIGHT":

File: B:CPM63.SYS Record: 00017 (0011H) LOF: 00068 (0044H)

       00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F    0123456789ABCDEF
       -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --    ----------------
0880 - C3 5C E7 C3 58 E7 7F 00 20 20 20 20 20 20 20 20   >C\gCXg.         <
0890 - 20 20 20 20 20 20 20 20 43 4F 50 59 52 49 47 48   >        COPYRIGH<
08A0 - 54 20 28 43 29 20 31 39 37 39 2C 20 44 49 47 49   >T (C) 1979, DIGI<
08B0 - 54 41 4C 20 52 45 53 45 41 52 43 48 20 20 00 00   >TAL RESEARCH  ..<
08C0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08D0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08E0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08F0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<

     Note the pattern of HEX 20's above.  At location 0887 (now 00h)
place the number of HEX bytes the command line will contain, in this
case, 5.  At location 0888 start the actual command.  The result is as
shown below:


File: B:CPM63.SYS Record: 00017 (0011H) LOF: 00068 (0044H)

       00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F    0123456789ABCDEF
       -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --    ----------------
0880 - C3 5C E7 C3 58 E7 7F 05 53 20 24 41 4C 20 20 20   >C\gCXg.S $AL    <
0890 - 20 20 20 20 20 20 20 20 43 4F 50 59 52 49 47 48   >        COPYRIGH<
08A0 - 54 20 28 43 29 20 31 39 37 39 2C 20 44 49 47 49   >T (C) 1979, DIGI<
08B0 - 54 41 4C 20 52 45 53 45 41 52 43 48 20 20 00 00   >TAL RESEARCH  ..<
08C0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08D0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08E0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<
08F0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   >................<

     Save this file again, and put it in place of your system tracks.
Now the next time you cold boot, the log in message will be meaningful
and you will automatically run "S $AL".

SUMMARY

     When you obtain a copy of "EDFILE.COM" make sure to obtain a copy
of the accompanying .DOC file, it is absolutely essential.  Another
feature I have not heretofore mentioned, EDFILE.COM has HELP features
built in!

     I also use this method of editing my CP/M system in order to test
my compiled Turbo Pascal files under different size operating systems
(saved on disk as CPM64.COM, CPM63.COM, CPM62.COM, etc.).  Additionally,
I have used this method to change my operating system (changed the
resident CP/M command "USER" to "U", logon procedures, autoload
functions, prompt messages, and different size operating systems with
new logical assignments for my disk drives.  Try this system and I don't
think you'll ever go back to using "XAMN.COM" or "DDT.COM" to modify
your .COM files again!