System information

Trace 10 (hexadecimal) steps
C0Z1M0E1I1 A-00 B-0800 D=0000 H=0121 S=0100 P=0100 MVI B,08
C0Z1M0E1I1 A-00 B-0000 D=0000 H=0121 S=0100 P=0102 MVI C,00
C0Z1M0E1I1 A-00 B-0800 D=0000 H=0121 S=0100 P=0103 LXI H,0119
C0Z1M0E1I1 A-00 B-0800 D=0000 H=0119 S=0100 P=0107 MOV A,M
C0Z1M0E1I1 A-02 B-0800 D=0000 H=0119 S=0100 P=0108 SUB C
C0Z1M0E1I1 A-02 B-0800 D=0000 H=0119 S=0100 P=0109 JNC 010D
C0Z1M0E1I1 A-02 B-0800 D=0000 H=0119 S=0100 P=010D INX H
C0Z1M0E1I1 A-02 B-0800 D=0000 H=011A S=0100 P=010E DCR B
C0Z1M0E1I1 A-02 B-0700 D=0000 H=011A S=0100 P=010F JNZ 0107
C0Z1M0E1I1 A-02 B-0700 D=0000 H=011A S=0100 P=0107 MOV A,M
C0Z1M0E1I1 A-00 B-0700 D=0000 H=011A S=0100 P=0108 SUB C
C0Z1M0E1I1 A-00 B-0700 D=0000 H=011A S=0100 P=0109 JNC 010D
C0Z1M0E1I1 A-00 B-0700 D=0000 H=011A S=0100 P=010D INX H
C0Z1M0E1I1 A-00 B-0700 D=0000 H=011B S=0100 P=010E DCR B
C0Z1M0E1I1 A-00 B-0600 D=0000 H=011B S=0100 P=010F JNZ 0107
C0Z1M0E1I1 A-00 B-0600 D=0000 H=011B S=0100 P=0107 MOV A,M*0108
Insert a "hot patch" into Program should have moved the
the machine code value from A into C since A>C.
0109 JC 100 to change the Since this code was not executed,
JNC to JC it appears that the JNC should
have been a JC instruction
010C
Stop DDT so that a version of
_GO the patched program can be saved
A>SAVE 1 SCAN.COM Program resides on first
page, so save 1 page.
A>DDT SCAN,COM
Restart DDT with the save memory
DDT VER 1.0 image to continue testing
NEXT PC
0200 0100
4.4 A Sample Program CP/M Operating System Manual
4-19