System information

Whenever the R command is issued, DDT responds with either the error indicator ? (file cannot
be opened, or a checksum error occurred in a HEX file) or with a load message. The load
message takes the form:
NEXT PC
nnnn pppp
where nnnn is the next address following the loaded program and pppp is the assumed program
counter (100H for COM files, or taken from the last record if a HEX file is specified).
4.2.9 The S (Set) Command
The S command allows memory locations to be examined and optionally altered. The S
command takes the form:
Ss
where s is the hexadecimal starting address for examination and alteration of memory. DDT
responds with a numeric prompt, giving the memory location, along with the data currently held
in memory. If you type a carriage return, the data is not altered. If a byte value is typed, the value
is stored at the prompted address. In either case, DDT continues to prompt with successive
addresses and values until you type either a period or an invalid input value is detected.
4.2.10 The T (Trace) Command
The T command allows selective tracing of program execution for 1 to 65535 program steps. The
T command takes the forms:
T
Tn
In the first form, the CPU state is displayed and the next program step is executed. The program
terminates immediately, with the termination address displayed as
*hhhh
where hhhh is the next address to execute. The display address (used in the D command) is set to
the value of H and L, and the list address (used in the L command) is set to hhhh. The CPU state
at program termination can then be examined using the X command.
4.2 DDT Commands CP/M Operating System Manual
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