System information

where d is the stop address. The machine state can be examined at this point using the X
(Examine) command. You must specify breakpoints that differ from the program counter address
at the beginning of the G command. Thus, if the current program counter is 1234H, then the
following commands:
G,1234
G400,400
both produce an immediate breakpoint without executing any instructions.
4.2.5 The I (Input) Command
The I command allows you to insert a filename into the default File Control Block (FCB) at
5CH. The FCB created by CP/M for transient programs is placed at this location (see Section 5).
The default FCB can be used by the program under test as if it had been passed by the CP/M
Console Processor. Note that this filename is also used by DDT for reading additional HEX and
COM files. The I command takes the forms:
Ifilename
Ifilename.typ
If the second form is used and the filetype is either HEX or COM, subsequent R commands can
be used to read the pure binary or hex format machine code. Section 4.2.8 gives further details.
4.2.6 The L (List) Command
The L command is used to list assembly-language mnemonics in a particular program region.
The L command takes the forms:
L
Ls
Ls,f
The first form lists twelve lines of disassembled machine code from the current list address. The
second form sets the list address to s and then lists twelve lines of code. The last form lists
disassembled code from s through address f. In all three cases, the list address is set to the next
unlisted location in preparation for a subsequent L command. Upon encountering an execution
breakpoint, the list address is set to the current value of the program counter (G and T
commands). Again, long typeouts can be aborted by pressing RETURN during the list process.
4.2 DDT Commands CP/M Operating System Manual
4-7