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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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