DDTZ v2.5
by C.B. Falconer
edited by George A. Havach
Introduction:
============
DDTZ v2.5 is a complete replacement for DDT, Digital Research's
famous Dynamic Debugging Tool, with improved functionality, bug ex-
termination, and full Z80 support. In general, DDTZ is fully compat-
ible with the original utility, but it has extra and extended commands
and many fewer quirks. All Z80-specific instructions can be (dis)as-
sembled, though in Intel rather then Zilog format. Furthermore, DDTZ
will correctly trace ('T' and 'U' commands) both 8080 and Z80 instruc-
tions, depending on which CPU is operating. On startup, the program
announces which CPU it is running on.
The program is invoked by typing
ddtz<ret>
or
ddtz [d:]filespec<ret>
In the second form, DDTZ will load the specified file into memory
starting at 0100H, unless it's a .HEX file that sets its own load ad-
dress. Besides reporting the NEXT free address and the PC (program
counter) after a successful load, DDTZ also shows the number of memory
pages needed for a SAVE. Instead of having to write all this down,
just use the 'Q' command at any time to redisplay these three values
for the current application.
As in DDT, when a program is loaded above the area holding the 'A'
and 'L' (and now 'K') command code, these commands are disabled, and
the extra memory is released to the user. Thus, DDTZ can occupy as
little as 3K total memory space. Unlike DDT, however, DDTZ will not
overwrite itself or the system on program loads (except .HEX files).
At initialization, the stack pointer (SP) points to a return to
DDTZ, just like for the CCP. Thus, programs that normally return to
the CCP will be returned to DDTZ. The 'B' command reinitializes this
condition.
The intercept vector copies the BDOS version number, etc., so an
object program does not know that DDTZ is running (except for BIOS-
BDOS vector size). Thus, programs that check the version number should
execute correctly under DDTZ.
All input parameters can now be entered in any of three formats:
(1) hexadecimal (as in DDT),
(2) decimal, by adding a leading '#' character,
(3) ASCII, by enclosing between either single or double quotes;
either one or two characters are allowed.
Leading blanks in command lines are absorbed. Either a comma or a
(single) space is a valid delimiter. Either uppercase or lowercase
input is accepted.
The default command (for anything not otherwise recognizable) is
'H'. This allows convenient calculation, along with the other features
described below. So, to convert a number, just enter it!
As in DDT, the prompt character is '-', and the only error message
is the query ('?'), which generally kicks you back to command mode.
New Commands (Over DDT):
=======================
@ Sets or shows (with no parameter) the internally stored "base"
value. Also used with the 'S' and 'D' commands as an optional
parameter (though without the '@') to display memory from an
arbitrary base marker (offset). When set to zero (the default),
it does not affect any screen displays.
B B)egin: resets the USER stack pointer to its initial value,
such that any program that exits by an RET will return to DDTZ.
DDTZ provides a default stack space of approximately 24 bytes
for user programs.
C C)ompare first_address,last_address,against_address: shows all
the byte differences between two memory areas, in the format
XXXX aa YYYY bb
where XXXX and YYYY are the comparative memory addresses, and
aa and bb are the corresponding byte values. Can be used to
verify the identity of two files by first loading them into
different memory areas with the 'R' command (see below).
K K)eep: stores the modified memory area to disk under the file-
name specified by the 'I' command, overwriting the original
file from which it was loaded (the user is queried before doing
so). By default, the image of memory from 0100H through the
"NEXT" value -1 is saved. "K first_address,last_address" over-
rides this and allows writing ANY memory area to a file. Almost
a necessity for CPM 3.0 (no SAVE!).
Q Q)uery: redisplays the "NEXT PC SAVE" report at any time.
W W)here first_address,last_address,value: searches the specified
memory area for the value (a 16-bit word, not a byte) and shows
the locations of all such. Very useful for finding CALL's or
JMP's to a particular address, etc.
Y Y)our_option parm1,parm2,address: executes an arbitrary routine
at the specified address, with the BC and DE registers set to
parm1 and parm2, respectively.
Z Displays (but does not alter) the Z80's alternate register set,
including the index registers (disabled if running on an 8080).
On Z80's, automatically included as the last part of the dis-
play by the 'X' command.
Based (Offset) Displays:
=======================
The 'D' and 'S' commands can use a stored base value (offset), as
set by the '@' command. The current @ value may be overridden for a
single execution of these commands by adding the base as an extra par-
ameter in the command line. The effect is to add this value to the
first/last address and display accordingly. The address listing on the
left becomes XXXX:YYYY, where XXXX is the offset address and YYYY is
the actual memory address being displayed. For example, if you have a
data area located at 42B7H and wish to preserve easy access, just
enter "@42b7". Now, "d0,3f" will dump memory starting at 4237H.
Further Changes from DDT:
========================
A A)ssemble now accepts the full Z80 as well as 8080 instruction
set, although it expects them in Intel rather than Zilog format
(see notes below under the 'L' command). When in doubt, try
poking in the hexcode (with the 'S' command) and then L)isting
to see what the (dis)assembler recognizes.
D D)isplay or D)ump will accept an optional third parameter to
set the base value for a single execution only. Format has been
cleaned up.
H H)ex_arithmetic on two values also shows their difference in
decimal. With only one value, converts to hexadecimal, decimal,
and ASCII (low-order byte only).
I I)nput now allows drive specification (d:...) and sets up the
complete command line, including the second FCB at address
006CH on. Note that the filename may be in lowercase.
L L)ist now displays the raw hexcode, especially handy when exam-
ining non-code areas. Intel (8080 style) mnemonics are used, so
some disassembled instructions may look a little strange. E.g.,
the Z80's 'IN B,(C)' and 'OUT (C),B' become 'INP B' and 'OUTP
B', respectively; 'LD (nnnn),BC' becomes 'SBCD nnnn', 'ADD IX,
BC' becomes 'DADX B', and 'JP (IX)' becomes 'PCIX'.
R R)ead now permits loading a file into memory with an offset,
which is added to the default load address of 0100H. When
reading in a .HEX file with a preset bias, the 'R' command
will not transfer control to an invalid execution point. Ano-
ther execution of the 'R' command will reread the input file,
e.g.:
i blah<ret>
r<ret>
...modify the code and generally mess about...
r<ret>
The original file is reloaded, and the modifications are re-
moved.
S S)ubstitute or S)et, like D)isplay, now accepts an optional
second parameter to set the base value for a single execution
only.
T T)rap/trace on termination now shows the complete CPU state.
Traps and traces no longer lock up when a user RST 7 instruc-
tion is executed. Tracing of BDOS/BIOS calls is heavily trun-
cated, avoiding clutter and preventing system crashes.
X eX)amine also shows what two-byte values the HL and SP regis-
ters are actually pointing to. On Z80's, displays the alternate
register set.
NOTE: Any use of the 'K' or 'R' command resets the system DMA trans-
fer address to the standard default value of 0080H.
