


          PCPATCH.TXT
          July 26, 1987
                       DOCUMENTATION FOR PC-PATCH version 1.0

               This   file  and  the  associated  program  PCPATCH.COM  are 
          copyrighted by:
                              Dragon Datasystems, Inc.
                              Deming, NM 87030
                              (505)546-3205 (voice)

          Both  may be freely copied for your personal use and  distributed 
          to  others,  via bulletin boards or public database services such 
          as  Compuserv or the Source,  provided no charge is made for  the 
          copy  (aside  from normal hourly rates on  databases  or  service 
          charges for bulletin boards and user groups).

               This  program  is  the result of a fruitless  search  for  a 
          simple patching program similar to the public domain PATCH.COM in 
          CP/M.  My need for such a program is due to not getting a copy of 
          DBUG  with  my XT clone.   (We got DDT with  the  CP/M  operating 
          system,  why  can't  Microsoft be so generous?)  The  program  is 
          written  in TurboPascal (version 3.0) and compiled on an XT clone 
          running  PC-DOS  v.  3.2.   I appologise for not giving  out  the 
          source  code  but  I  made extensive  use  of  Robert  Jourdain's 
          assembler  language  subroutines from Turbo Pascal  Express  (the 
          Brady division of Simon & Schuster, (c) 1987) so fork over $40 or 
          so to your local bookstore and get your own copy.  If you do  any 
          amount  of Turbo Pascal programing these routines are well  worth 
          it; the increased speed of screen i/o is amazing.

               I  have been playing with computing machines since the  days 
          of  vacuum tubes and consider myself reasonably competent to read 
          technical material,  however,  after studying a variety of books, 
          including  those by Microsoft and Big Blue,  I find that I cannot 
          comprehend  the memory allocation of MS-DOS (or  PC-DOS).   As  a 
          consequence this program was written using an empirical approach. 
          After  the  first  part of the program was  written  (to  examine 
          memory)  I went browsing around my 640k and it seems that the 64k 
          starting at segment 5000h and offset 0100h wasn't being used  for 
          anything  I  was doing.  (This may not be true for  you  so  look 
          before  you load.) So I decided that that was as good a place  as 
          any  to load the file I wished to modify (any better ideas  would 
          be  greatly appreciated).   If this isn't convenient for you send 
          me  $20  and tell me where to put it (or any  other  comments  or 
          suggestions)  and I will send you the latest version (let me know 
          your disk format and storage location requirements).




















          PCPATCH.TXT -- page 2

               The  program  is pretty simple to operate and  largely  self 
          guided.  It uses the IBM style cursor keys namely:

               left arrow     -- 27 75 (decimal)  )    moves cursor
               right arrow    -- 27 77            )    around
               up arrow       -- 27 72            )    memory
               down arrow     -- 27 80            )    display
               home           -- 27 71  restarts memory display
               end            -- 27 79  ends the program
               page up        -- 27 73  decreases the offset by 256
               page down      -- 27 81  increases the offset by 256
          and
               esc            -- 27 toggles window showing control codes:
               ^E             -- 5  Edit (change) a byte
               ^O             -- 15 allows resetting the Offset
               ^C             -- 3  allows Changing both segment & offset
               ^L             -- 12 Loads a file into memory @ 5000h:0100h
               ^S             -- 19 Saves a file to disk from 5000h:0100h
               ^X             -- 24 eXits program to dos

               The  display  is in both hex and ascii but entry  of  memory 
          changes must be in hex.
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