Table of Contents
Advertisement
Section B:
Hardware interface
*************************************************************~**********
*
*
*
9 - Select Drive
*
*
*
************************************************************************
On entry:
C
E
On exit
HL
Drive Number
Access Bit
Error code
The
drive
passed in register C is defined as reference drive
for
all
future disk read/write operations.
A value of
11
0
11
in C refers to
drive
A,
a
11
1"
to drive B and so forth up to "15" for drive
P.
The
least
significant bit in register E specifies whether this is the first access
to
that
drive;
if it is reset,
the drive parameters have to
be
re-
determined.
In
this
case,
an
eventual disk access is
necessary
to
determine the recording format.
If the "first-access" bit is set,
only
some
internal variables are assigned new values,
no disk
access
will
occur.
After a successful disk select operation, HL is returned with
a
non-zero
value.
If
the desired drive is not defined or an error was encountered
during determination of the drive parameters, HL is zero on return.
The access bit in register E is an enhancement over CP/M 2.2 and DiCOS.
Example:
Select drive B: without re-determining the drive parameters
LD
C,S!iJ
EOS function code
LD
DE,PARAMS
Parameters
CALL
5
Call EOS
LD
A,H
OR
L
Check if o.k.
JP
Z,SELERR
Zero
=
no success
PARAMS:
DB
9
Hardware function No.
DB
~
ow
'B'-'A'
Drive B
=
number
1
ow
1
prevent redetermination
DW
~
EOS System manual
Daeumling & Zimmermann
Page 145
Advertisement
Chapters
Table of Contents
