Command Setup and Execution Under CPIM-86
TRANSIENT
PROGRAM
LOAD
Like
CP/M-80,
the
CCP
in
CP/M-86
parses up
to
two file names following the
command
and
places the properly fomatted File
Control
Blocks (FCBs)
at
loca-
tions
005CH
and
006CH in the base page relative
to
the DS register.
Under
CP/M-80,
the default
DMA
address
is
initialized to 0080H in the base page.
However, due
to
the segmented memory
of
the 8086 processor, the
DMA
address
is
divided into two parts: the
DMA
segment address the
DMA
offset. Therefore,
under
CP/M-86,
the default
DMA
base
is
initialized
to
the value
of
DS,
and
the
default
DMA
offset
is
initialized
to
0080H. Thus,
CP
/M-80
and
CP
/M-86
operate
in the same way:
both
assume the default
DMA
buffer occupies the second
half
of
the base page.
TRANSIENT
PROGRAM
EXIT
The
CCP
transfers control
to
the transient
program
through an 8086
"Far
Call".
The transient program may exit in one
of
three ways.
•
It
can use the 96-byte
CCP
stack
and
return directly to the
CCP
upon
program
termination by executing a
"Far
Return".
If
BDOS calls are
to
be
made, the transient program requires its own stack.
• Program termination can occur when BDOS function 0
is
executed. Func-
tion
0 can terminate a
program
without removing the
program
from
memory
or
changing the memory allocation state (see Chapter 4).
• The
operator
can terminate
program
execution by pressing
CONTROL-C
during line edited input. This has the same effect as the
program
executing
BDOS function
O.
No disk reset occurs
and
the CCP
and
BDOS modules are
not reloaded from disk
upon
program
termination.
2-9
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