CP/M   V2.2
                              Application Note 07, 2/20/82
                           Changing the Restart Number in DDT

                          Copyright   1982 by Digital Research
                   CP/M is a registered trademark of Digital Research.
                         DDT is a trademark of Digital Research.
                                 Compiled November 1982

          Applicable products and version numbers:  CP/M    V1.4,  V2.0,  V2.1,
          and V2.2

          Program:  DDT.COM

               DDT   uses RST 7 (machine instruction 0FFH) to set break points.
          To  change the restart number, modify the three bytes indicated by ??
          in  the  following  procedure  for  a  new  restart  instruction  and
          location.  The  restart  instruction  uses  the bit pattern 11XXX111,
          where XXX is the restart number you use.  (AFH is RST 1, B7H  is  RST
          2,  and  BFH  is RST 3.)  The restart location is usually the restart
          number times 8.  Do not use RST 0 because it is reserved for CP/M.

               The following procedure applies to DDT supplied with  CP/M  V2.1
          and  V2.2.  For V1.4 and V2.0, change the instructions at 19B and 19E
          to the following:

                  019B  sta  fe4
                  019E  sta  10ee

               Make a back-up copy of DDT.COM before you use DDT  to  make  the
          following changes:

                  A>ddt ddt.com
                  DDT VERS 2.2
                  NEXT  PC
                  1400 0100
                  -l103
                    103  JMP  013D
                          .
                          .
                          .
                  -a103
                  0103  jmp  18b
                  -a18b
                  018B  lhld 1ec
                  018E  shld 8e7
                  0191  inx  h
                  0192  shld 8ed
                  0195  lda  1eb
                  0198  sta  ad5



                                          1

          CP/M V2.2                                     Application Note 07


                  019B  sta  fea
                  019E  sta  10f4


                  01A1  jmp  13d
                  - s1ec
                  01EB ?? f7
                  01EC ?? 30
                  01ED ?? 00
                  01EE ?? .
                  -g0
                  A>save 19 ddt6.com


               To change the restart number for DDT in the future, modify  only
          the 3 bytes 1EBH, 1ECH and 1EDH.

               Licensed  users  are  granted  the  right   to   include   these
          modifications in CP/M software.