Apple Logic Board Información técnica descargar pdf (Pagina 20)

to run these programs with the relocated DOS. The program called

MOD, included in the software package with the Saturn 64K and

128K boards will repair this bug so that both FID and MUFFIN will

run with the relocated DOS as well as the normal DOS.

In addition to modifying FID for use with the relocated DOS,

MOD will also make necessary changes to FID so that it can be

used with the DOS PSEUDO—DISK (see Chapter 6). The modified FID

can be used as a direct replacement for FID (as distributed on

the DOS 3.3 system master), with or without the PSEUDO—DISK, or

the relocated DOS.

B. MODIFICATION OF BOOTl3

Modification of the program BOOTl3, provided on the DOS 3.3

system master, is required for proper operation with DOS 3.2

disks initialized under the relocated DOS. MOD will make the

required changes to BOOTl3 to allow use with the relocated DOS.

V. TECHNICAL INFORMATION

A. RELOCATED DOS OPERATION

As described previously, the program called MOVEDOS does

exactly what its name implies; it moves the existing DOS (ver 3.2

or 3.3) present at the top of the 48K of user RAM ($9~OO—$BFFF)

into the Saturn 64K or 128K board. In addition to being able to

maintain DOS in the RAM board, the alternate BASIC may reside

there as well (Integer BASIC on an Apple II plus, Applesoft on an

Apple II). This is possible because DOS is moved (by MOVEDOS)

into the second 16K bank of the RAM card (not used by BASIC). All

but 4K of this 16K bank is used by the relocated DOS and

associated monitor routines. The unused 4K portion of the second

16K bank of the Saturn board will be used by future software

packages supporting the 64K and 128K RAM boards.

Now, when a DOS command is invoked from Applesoft, Integer

BASIC, a machine language routine or the keyboard, it is executed

by the relocated DOS present in the Saturn RAM board. A small

portion of DOS is maintained within the lower 48K of RAM from

$BEOO to $BFFF. This part of DOS includes a short routine which

serves to enable (turn on) the required part of the Saturn 64K or

128K board which contains most of DOS, when DOS is called. The

DOS command is then executed by the relocated DOS in the RAM

board, after which time this part of the Saturn RAM board is

disabled, and the s/stem is returned to the state it was in prior

to the call to DOS. The routines which enable the second bank of

the Saturn 64K and 128K boards (containing DOS), as well as

disable it when through, are located at the top of the user RAM

from $BEOO to $BFFF, occupying 1/2 K. HIMEM is set to reflect

this.

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