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dos #17
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2022-08-26
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DOS AND DON'TS -- Part 17
{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}{CBM-T}
Now you want to know how to get data
off of the disk. Well this is done
with the U1 command. The process is
almost exactly opposite of putting
data onto the disk.
As usual, we have to OPEN two
channels -- one to send commands and
one to RECEIVE the data. We can use
the same OPEN statements as before for
this.
After we have our files open, all
we have to do is decide where we are
going to get our data from. Now this
can be any legal track and sector.
Check the first table in this article
for more info. on tracks and sectors.
Most people will develop their own
schemes for saving their data on the
disk and the READING process will be
according to this layout.
After we have decided where to get
the data from we must tell the
computer to go to the disk drive and
get it. This is done with the U1
command. The syntax of the U1 command
is the same as that of the U2 command.
We must tell the U1 command what
channel to PUT the data into, what
drive to access, and what track and
sector to get the data from.
After the U1 command is executed,
data from that particular block and
sector will be contained in the buffer
specified. All you have to do then is
GET the data from that buffer. This
is acomplished with the GET# command.
A short example of all of this is
shown below. It is assumed that the
data we want is on track 10, and
sector 15 since this is where we tried
to put our data is the above examples.
10 OPEN15,8,15
20 OPEN2,8,2,"#"
30 :
40 TR=10 : SE=15
50 :
60 PRINT#15,"U1:"2;0;TR;SE
70 :
80 FOR X = 1 TO 255
90 GET#2,A$
100 PRINT A$;
110 NEXT X
120 :
130 CLOSE2:CLOSE15
140 END
This example reads in the data on
track 10, sector 15 and then prints
the data to the screen. You could
of course, save the data in an array
or however you would like to store it.
As added examples there are two
programs included on this disk. One
program allows you to print up to 80
characters to track 10, sector 15.
Please do not run this program on a
LOADSTAR disk unless you are willing
to lose its contents. This program MAY
write over other data on the disk that
is needed. Try the program on a new,
formatted disk.
The second program reads track 10,
sector 15 and then asks you for a
PASSWORD. The program then compares
what the user types in with what
appears on track 10, sector 15. Using
this technique, you can put in some
protection for any of your programs.
The program to write on the disk
is named 'WRITE' and the program to
check the pass-word is called 'READ'.
They are both on SIDE 2 of LOADSTAR
NUMBER 7.
Hope you have learned something from
all of this. Go out and have fun.
--------------------------------------