System information

4.2 DDT Commands
The individual commands are detailed below. In each case, the operator must wait for the hyphen
prompt character before entering the command. If control is passed to a program under test, and
the program has not reached a breakpoint, control can be returned to DDT by executing a RST 7
from the front panel. In the explanation of each command, the command letter is shown in some
cases with numbers separated by commas, the numbers are represented by lower-case letters.
These numbers are always assumed to be in a hexadecimal radix and from one to four digits in
length. Longer numbers are automatically truncated on the right.
Many of the commands operate upon a CPU state that corresponds to the program under test. The
CPU state holds the registers of the program being debugged and initially contains zeros for all
registers and flags except for the program counter, P, and stack pointer, S, which default to 100H.
The program counter is subsequently set to the starting address given in the last record of a HEX
file if a file of this form is loaded, see the I and R commands.
4.2.1 The A (Assembly) Command
DDT allows in-line assembly language to be inserted into the current memory image using the A
command, which takes the form:
As
where s is the hexadecimal starting address for the in-line assembly. DDT prompts the console
with the address of the next instruction to fill and reads the console, looking for
assembly-language mnemonics followed by register references and operands in absolute
hexadecimal form. See the Intel 8080 Assembly Language Reference Card for a list of
mnemonics. Each successive load address is printed before reading the console. The A
command terminates when the first empty line is input from the console.
Upon completion of assembly language input, you can review the memory segment using the
DDT disassembler (see the L command).
Note that the assembler/disassembler portion of DDT can be overlaid by the transient program
being tested, in which case the DDT program responds with an error condition when the A and L
commands are used.
4.1 Introduction CP/M Operating System Manual
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