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EXAMPLE
Th-is example illustrates how one might configure the
64KZ card for use in a Cromemco Disc Operating System (CDOS).
With a 64KZ card in the system, CDOS would typically be
confiqured with proqram CDOSGEN to use all available 64
Kbytes of read/write memory. The CDOS program is transferred
("booted") from maqnetic diskette to read/'N'rite memory for
execution by RDOS, a program spanning addresses C0008 - C3FFH
and resident in ROM memory on the Cromemco 4FDC Floppy Disc
Controller card.
The sequence of events for a CDOS boot are:
(1) RDOS reads a loader program from the first diskette
sector into read/write memory area 0080H - 0100H.
(2) A jump to 0080H is then executed.
(3) The loader program at 0080H - 0100H first enables memory
BANK 0 only, then completes the transfer of CDOS from
diskette to rouqhly the uppermost 8 Kbytes of read/write
memory.
Switch settings on the 4FDC card allow the user options
of completely disabling or enabling RDOS; of removing or
retaining RDOS in the memory map after a CDOS boot; and of
"coming up" in RDOS after several console RETURN keystrokes
a nd boot i ng CDOS only when the direct command "B" (Boo t) is
i ss ued, 0 r aut 0mat i call y ex e cut i ng the RDOS boo t r 0uti ne i n
response to several console RETURN key strokes.
P-.ssuming the 4FDC and 64KZ switch settings shown in
Figure 1. CDOS automatically boots up after each system RESET
or P.O.C. ','<'hen the console RETURN key is depressed several
times. The rationale behind the switch settings follows.
First, BLOCK B, which is assiqned to the upper 32K of memory,
must disable after a RESET or P.O.C. to avoid a conflict with
the shadowed RDOS ROM proqram located at C000H - C3FFH. This
is accomplished by setting 64KZ switch RESET B =OUT. 4FDC
switch number 2 must be positioned ON so as to disable RDOS
after boot (RDOS is disabled at the same time memory BANK 0
is enabled). 4FDC switch number 3 is positioned ON to
automatically start the RDOS boot routine after several
RETURN key strokes, and finally 64KZ switch BLOCK B, BANK 0
=IN so as to activate the upper 32 Kbytes of read/write
memory as RDOS is disabled. The resulting memory map after
CDOS has been loaded into 64KZ memory is shown.
