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Digital Research
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Sepp J Morris
2020-11-06 18:50:37 +01:00
parent 621ed8ccaf
commit 31738079c4
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CPM OPERATING SYSTEMS/CPM 2.X/CPM 2.2/PATCHES/CPM22APN.10 Normal file
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CP/M V2.2
Application Note 10, BDOS, 03/12/82
Booting CP/M on Drives Other Than Drive A
Copyright 1982 by Digital Research
CP/M is a registered trademark of Digital Research.
DDT is a trademark of Digital Research.
Compiled November 1982
Applicable products and version numbers: CP/M V2.2
Module: BDOS
Booting CP/M on a drive other than drive A changes the initial
prompt displayed after a cold boot. Instead of A>, you must specify
the drive intended to follow the cold boot in the following patch
procedure. Also, your BIOS must pass the intended boot drive to
register C in the CCP upon cold boots (see the CP/M Operating System
Manual). The intended boot drive in this patch procedure and in your
BIOS is indicated by a number relative to zero. (A=0, B=1, C=2, ...,
P=15.) This procedure changes the drive selected by BDOS Function 13
(Reset Disk System).
Use caution installing this patch because it requires
modification to the CP/M submit processor (SUBMIT.COM). SUBMIT must
write the $$$.SUB file to the boot drive you specify in this patch.
The procedure to modify SUBMIT is described in CP/M V2.2, Patch 03,
dated 1/21/82. Instead of setting the byte at 5BBH to 1, as
described in Patch 03, set the byte to the specified boot drive plus
1. For example, if the boot drive is 1 (the B drive), then set the
byte in SUBMIT.COM at 5BBH to 2.
Place the following code in a file named CPMxx.COM (xx = memory
size). Determine the CP/M base for your size memory and include it
in the code. Assemble and insert CPMxx.COM into the SYSGEN or MOVCPM
image exactly as you would patch in a new version of your BIOS. Use
the DDT i command followed by the DDT r command. Use the same
offset as your custom BIOS. Make a back-up copy of CPMxx.COM before
you make the changes.
cpmbase equ ?
drive equ ? ;boot drive
;0=A, 1=B, ..., 15=P
org cpmbase + 0148Ch
jmp cpmbase + 15EEh ;was "xra a"
org cpmbase + 15EEh
mvi a,drive ;was "nop"
sta cpmbase + 0B42h ;was "nop"
jmp cpmbase + 1490h ;was "nop"
Licensed users are granted the right to include these changes in
CP/M V2.2 software.