BLOCK-WRITE
The purpose
of
a BLOCK-WRITE
is
to
save the contents
of
a
file
buffer into a
specified sector. It
is
thus the reverse
of
the
BLOCK-READ command. Although the
BLOCK-WRITE command (B-W)
is
still part
of
the DOS command set,
it
is
nearly
always replaced by the
U2
command.
FORMAT FOR THE BLOCK-WRITE COMMAND:
PRINT#15, "U2";channel #;drive #;track #;sector #
where "channel
#"
is
the channel number specified when the
file
into which the block
will be read was opened; "drive
#"
is
the
drive number; and "track
#"
and "sector
#"
are respectively the track and sector numbers that should receive the block
of
data being
saved from the file buffer.
ALTERNATE FORMATS:
PRINT#15,"U2:"channel
#;drive #;track #;sector #
PRINT#15,"UB:"channel
#;drive #;track #;sector #
PRINT#15,"U2:channel
#,drive
#,track
#,sector
#"
EXAMPLES:
To restore track 18, sector 1
of
the directory from the disk buffer filled
by
a BLOCK-
READ, use:
PRINT#15,'
'U2'
';5;0;18;1
You'll return
to
this example on the next page, after you learn
to
alter
the
directory
in
a
useful way.
You can also
use
a BLOCK-WRITE
to
write a name
in
Track
1,
Sector I, a rarely-
used sector. This can be used
as
a way of marking a diskette as belonging
to
you. Here
is
a
program
to
do it, using the alternate form
of
the BLOCK-WRITE command:
110 INPUT"YOUR NAME";NA$
120 OPEN 15,8,15
130 OPEN
4,8,4,"#"
140
PRINT#4,NA$
150 PRINT#15,"U2";4;0;1;1
160 CLOSE 4
170
CLOSE
15
180 END
69
Enter a name.
Open command channel.
Open direct access channel.
Write name
to
buffer.
Write buffer
to
Track
1,
Sector I
of
diskette.
Tidy
up
after.
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