CHAP04.TXT
                         Version 1.01 12/27/84
                        Robert Flagg 72466,2332

                         Chapter 4 - Patching

         Even  where a program cannot be easily overlaid,  it  is
often  possible  to  configure it for a  particular  computer  or
function    by    changing   the   object   code    byte-by-byte.
Overlaying is a fast way of making many such changes,  but it  is
cumbersome  and  unnecessary where only a few changes need to  be
made. Making changes in this manner is called "patching".

         DDT may be used for examining and changing the values at
each  address in the program,  with its "s"  (Set)  command.  For
example, a common patch is changing the cursor delays in WordStar
3.3 (WS.COM):

         A>DDT WS.COM <cr>
         DDT VERS 2.2   <---returned by the command
         NEXT PC        <---returned by the command
         4800 0100      <---returned by the command
         -s02AF         <---the command and starting address (HEX)
         -02AF 03 **    <---returned by command - option to change **
                        <---the ** does not appear on your screen
                        <---Changing the delays:  (note that the
                            delays are DECIMAL!)

          Hex Old New
          Add.
         -02AF 03 01    <---(cr) makes the change and
         -02B0 09 03    <---moves to next address (HEX)
         -02B1 19 09    <---change next delay
         -02B2 40 19    <---
         -02B3 09 03    <---last delay
         -02B4 00       <---(cr) keeps data unaltered
         -02B5 00       <---(.) exits "s" mode
         -g0            <---exit from DDT

         WARM BOOT      <---system response

         A>SAVE 72  WSNEW.COM


         DDT was created in 1976 by Digital Research. Much easier
screen-oriented  patching  tools have been developed since  then.
Notable  examples  in the public domain are EDFILE and  its  very
recent offspring, PATCH.

         The  following is an example of invoking EDFILE for  the
purpose  of  examining the file  PATNEW.COM.  PATCH  is  similar,
except  that  it  is much more screen  oriented,  making  use  of
hilighting  and also using the standard WordStar cursor  movement
control keys (^X,  ^S,  ^D,  etc.). PATCH also allows you to edit
memory (and in versions 1.5 and above -track-by-track on any disk
drive!)

.PO 5

A>edfile c:patnew.com


Vers: 01-10-84; by: J.C.Kaltwasser & M.J.Mosko, K3RL

File: C:PATNEW.COM  Record: 00001 (0001H)   LOF: 00171 (00ABH)
      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F   0123456789ABCDEF
      -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --   ----------------
0180- 65 74 69 74 00 00 00 00 00 00 00 04 1B 3D 00 00  >etit.........=..<
0190- 64 00 1B 6C 2F 63 00 1B 2F 6C 63 01 20 20 04 03  >d..l/c../lc.  ..<
01A0- 0A 00 01 1A 2A 40 23 00 00 11 00 00 00 00 02 1B  >....*@@#.........<
01B0- 45 00 00 00 02 1B 52 08 00 00 0A 00 02 1B 54 00  >E.....R.......T.<
01C0- 00 00 02 1B 29 34 00 00 02 1B 28 30 00 00 0A 00  >....)4....(0....<
01D0- 7E B7 37 C8 23 F5 E5 7E CD 00 02 E1 F1 3D C8 18  >~77H#ue~M..aq=H.<
01E0- F3 CD 25 02 0D 0A 00 C9 C5 D5 E5 DD E5 FD E5 F5  >sM%....IEUe]e}eu<
01F0- 6F 26 00 E5 CD A6 00 F1 FD E1 DD E1 E1 D1 C1 C9  >o&.eM&.q}a]aaQAI<

?<cr>
File: C:PATNEW.COM  Record: 00002 (0002H)   LOF: 00171 (00ABH)
      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F   0123456789ABCDEF
      -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --   ----------------
0200- 6F E5 CD A6 00 C9 FE 80 DC 90 02 D4 A9 02 E6 7F  >oeM&.I~.\..T).f<
0210- 18 EE C5 D5 E5 DD E5 FD E5 CD A3 00 7D 18 D9 E5  >.nEUe]e}eM#.}.Ye<
0220- 21 06 02 18 04 E5 21 00 02 22 38 02 E1 E3 F5 C5  >!....e!.."8.acuE<
0230- D5 7E 23 B7 28 07 E5 CD 00 02 E1 18 F4 D1 C1 F1  >U~#7(.eM..a.tQAq<
0240- E3 C9 7D B4 C8 3A 24 01 87 87 87 E3 E3 E3 E3 C5  >cI}4H:$....ccccE<
0250- 01 D2 04 C1 3D 20 F4 2B 18 E8 CD D0 01 D8 2A CE  >.R.A= t+.hMP.X*N<
0260- 01 18 DF F5 C5 D5 E5 21 A8 01 CD 5A 02 21 A2 01  >.._uEUe!(.MZ.!".<
0270- CD D0 01 2A BA 01 D4 42 02 E1 D1 C1 F1 C9 F5 C5  >MP.*:.TB.aQAqIuE<

?Q <cr>
.PO 8

         As  you can see,  a <cr> takes you through the file  one
page at a time.  Both HEX and ASCII are dumped to the screen, and
finding an address is simply a matter of reading across and down.
Both  EDFILE  and PATCH allow you to edit either the HEX  or  the
ASCII  columns and both allow writing of the edited file back  to
the disk by a simple write command,  thus eliminating those pesky
"SAVE"  sizes!  A  very useful feature of these programs  is  the
ability to search through a file for HEX and/or ASCII strings.

         PATCH version 1.5 is available on the KayPro SIG in DL1.
There  are several files:  PAT15.BIN(COM),  the object code file,
PAT15.DOC,  the documentation and three files used for installing
the  program  on your  system:  PATINS.BIN(COM),  the  installer,
PAT15.INS,  the installation message file and PAT15.DTA, a binary
data file containing data on about 30 common terminals, including
KayPro with and without hilighting!