System information

Table 4-2. (continued)
Command
Character Result
A enters assembly-language mnemonics with operands.
S substitutes memory values.
T traces program execution.
U untraced program monitoring.
X examines and optionally alters the CPU state.
The command character, in some cases, is followed by zero, one, two, or three hexadecimal
values, which are separated by commas or single blank characters. All DDT numeric output is in
hexadecimal form. The commands are not executed until the carriage return is typed at the end of
the command.
At any point in the debug run, you can stop execution of DDT by using either a CTRL-C or G0
(jump to location 0000H) and save the current memory image by using a SAVE command of the
form:
SAVE n filename. COM
where n is the number of pages (256 byte blocks) to be saved on disk. The number of blocks is
determined by taking the high-order byte of the address in the TPA and converting this number to
decimal. For example, if the highest address in the TPA is 134H, the number of pages is 12H or
18 in decimal. You could type a CTRL-C during the debug run, returning to the CCP level,
followed by
SAVE 18 X. COM
The memory image is saved as X.COM on the disk and can be directly executed by typing the
name X. If further testing is required, the memory image can be recalled by typing
DDT X.COM
which reloads the previously saved program from location 100H through page 18, 23FFH. The
CPU state is not a part of the COM file; thus, the program must be restarted from the beginning
to test it properly.
4.1 Introduction CP/M Operating System Manual
4-3