Radio Shack TRS-80 Trsdos & Disk Basic Reference Manual page 43

TRSDOS Commands
In
this
display, register
B
contains the
hex
value
OA, and
register
C
contains 3E.
Taking
the
BC
register pair as a
pointer,
it
points to
address
0A3E.
Therefore, the contents of
memory
locations
0A3E
through
0A4D
are
shown
to the right of the
BC = 0A3E
=>marker.
In
this case,
address
0A3E
contains 09,
0A3F
contains
BA,
etc.
The
flag registers
F
and
F' are
handled
differently.
For
these
registers,
the
hex
contents of
the flag register
is
displayed, along with
a bit-by-bit alphabetic
code which makes
it
easier to interpret the
flag status.
For
example,
bit 7 (leftmost
bit)
is
the
sign
bit,
so the
alphabetic
code shows
an S
in that position
whenever
this bit
is
"set".
Here's
a
complete
table of codes
for
all
the
flag
bits:
if
not
set
bit status
if
s<
7 Sign S
6
Zero
z
5
unused
1
4
Half-carry
H
3
unused
1
2 Parity/overflow
P
1
Negative
N
Carry
C
In the
above
display,
none
of the
F
flag bits are set
(discounting the
unused
bits 5
and
3),
and
all
of the F'
flag bits are
set.
Notice the four
additional
lines
below
the
PC
register display.
Each
line
shows
the
contents of 16
bytes, starting
at
the address to the
left
of the arrow; the four
lines
always
show
a total
of
64
bytes of
contiguous
memory
i.e.,
locations
with
sequential addresses.
The
starting
point
in this four-line display
is
either
0000
or the
last
command
you
specified with the
D
command
(more
later.)
The
blank
area in the
lower
left
of the Display
is
where
commands
you
enter
will
be
displayed.
4-5