Tandy TRS-80 Owner Manual & Programming Manual page 71

TECHNICAL INFORMATION
If all
the
bits
contain
0,
no
error
occurred. (See the disk service
manual
for
further
details
on
the error
bits)
After returning
from
DSKCON,
you
can turn
off
the drive
motor by
putting the value
of
in
the
memory
location
FF40
(hex).
Sample Programs Using
DSKCON
This program
uses
DSKCON
to
restore the
head
to
track
0:
R
LDX $C00G
SET
X
AS
A
POINTER
TO THE
PARAMETERS
CLR
,){
DCOPC
=0 FOR
RESTORE
LDA 9\
DCDRO
=1 TO SELECT DRIVE
ONE
STA
1
»x
JSR ttcoaa] CALL DSKCON
IDA #$0Q TURN OFF THE DRIVE MOTOR
STA
$FF40
TBT
G
tX
CHECK FOR ERRORS
BNE
ERRORS
GO
REPORT
THE ERRORS
RTS
LDA
*$i)5
"E"
FOR ERROR
STA
*41D
TOP RIGHT
OF THE DISPLAY
RTS
This program
uses
DSKCON
to
read track
3,
sec-
tor 17 of
drive
into
memory
locations
3800
through 38FF:
LDX $C00B
LDA
*2
STA
,X
CLR
1
tX
LDA «3
STA 2,X
LDA *17
STA
3.X
LDU **3B00
SET
X
AS
A
POINTER
TO THE
PARAMETERS
DCOPC
= 2
FOR READ
A
SECTOR
SELECT DRIVE
SELECT TRACK
3
SELECT SECTOR
17
DCBPT=3B00(HEX)
FOR
STORING DATA
STU a,x
JSR
[*C004]
CALL DSKCON
LDA
»$00
TURN OFF THE DRIVE MOTOR
STA
SFF40
TST BtX CHECK FOR ERRORS
BNE
ERRORS
GO REPORT
THE
ERRORS
RTS
LDA
**45
STA $aiD
RTS
"E"
FOR ERROR
TOP RIGHT
OF
THE DISPLAY
C
Note:
DSKCON
preserves
the contents of all registers
except
CC.
You
can
write a similar
program
to
write
to
a
sec-
tor
by
setting
DCOPC
to
3 instead of
2.
Saving a Machine-Language
Program
You
can use
the
SAVEM
command
to
store a
machine-language program on
disk.
You
need
to
specify
where
in
memory
the
program
resides
(its
starting
and
ending
addresses).
You
also
need
to
specify the address
where
it
should be
executed.
Use
the
hexadecimal numbers
for
all
of
these
addresses.
For example,
let's
assume you have
a
machine-
language program which
resides in
addresses
5000-5FFF
of
memory. The
address
where
it
should be executed
is
500A.
You would
store this
program
on
disk
by
typing:
SAVEM "PROG/MAC"
>
&H5000
,
&H5FFF
,
1H500A
To load
it
back
into
memory, you
could use the
LOADM
command:
LOADM "PROG/MAC"
This would
load
"PROG
MAC"
back
into
memory
locations
5000-5FFF. The Computer
would
begin
executing
it
at location
500A.
If
you want
to
load
it
into
a
different
memory
loca-
tion,
you
could
specify
an
offset
address
to
add
to
the program's loading address. For example:
LOADM "PROG/MAC"
,
1000
would
load
"PROG/MAC"
into
memory
locations
6000-6FFF.
The Computer
would
begin executing
it
at
address 600A.
61