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58 lines
2.9 KiB
Plaintext
58 lines
2.9 KiB
Plaintext
CP/M V2.2
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Application Note 10, BDOS, 03/12/82
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Booting CP/M on Drives Other Than Drive A
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Copyright 1982 by Digital Research
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CP/M is a registered trademark of Digital Research.
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DDT is a trademark of Digital Research.
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Compiled November 1982
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Applicable products and version numbers: CP/M V2.2
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Module: BDOS
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Booting CP/M on a drive other than drive A changes the initial
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prompt displayed after a cold boot. Instead of A>, you must specify
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the drive intended to follow the cold boot in the following patch
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procedure. Also, your BIOS must pass the intended boot drive to
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register C in the CCP upon cold boots (see the CP/M Operating System
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Manual). The intended boot drive in this patch procedure and in your
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BIOS is indicated by a number relative to zero. (A=0, B=1, C=2, ...,
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P=15.) This procedure changes the drive selected by BDOS Function 13
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(Reset Disk System).
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Use caution installing this patch because it requires
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modification to the CP/M submit processor (SUBMIT.COM). SUBMIT must
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write the $$$.SUB file to the boot drive you specify in this patch.
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The procedure to modify SUBMIT is described in CP/M V2.2, Patch 03,
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dated 1/21/82. Instead of setting the byte at 5BBH to 1, as
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described in Patch 03, set the byte to the specified boot drive plus
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1. For example, if the boot drive is 1 (the B drive), then set the
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byte in SUBMIT.COM at 5BBH to 2.
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Place the following code in a file named CPMxx.COM (xx = memory
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size). Determine the CP/M base for your size memory and include it
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in the code. Assemble and insert CPMxx.COM into the SYSGEN or MOVCPM
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image exactly as you would patch in a new version of your BIOS. Use
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the DDT i command followed by the DDT r command. Use the same
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offset as your custom BIOS. Make a back-up copy of CPMxx.COM before
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you make the changes.
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cpmbase equ ?
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drive equ ? ;boot drive
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;0=A, 1=B, ..., 15=P
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org cpmbase + 0148Ch
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jmp cpmbase + 15EEh ;was "xra a"
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org cpmbase + 15EEh
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mvi a,drive ;was "nop"
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sta cpmbase + 0B42h ;was "nop"
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jmp cpmbase + 1490h ;was "nop"
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Licensed users are granted the right to include these changes in
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CP/M V2.2 software.
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