Commodore 1581 - Block-Write Command

EXAMPLES:
To restore track 40, sector 3 of the directory from the disk buffer
filled by a BLOCK-READ, use:
PRINT#15,"U2";5;0;40;3
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 1, 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$ Enter a name.
120 OPEN 15,8,15 Open command channel.
130 OPEN 4,8,4,"#" Open direct access channel
140 PRINT#4,NA$ Write name to buffer.
150 PRINT#15,"U2";4;0;l;l Write buffer to Track 1,
160 CLOSE 4 Sector 1 of diskette.
170 CLOSE 15 Tidy up after.
180 END
As with the BLOCK-READ command, there is a BLOCK-WRITE com
mand identical in function to "U2" that does not check the track and
sector parameters for valid bounds before attempting to write the
sector. Its format is:
PRINT#15,"B-on;channel #;drive #;track #;sector #
(The character after the B- is a shifted W.)
or
PRINT#15,uB-";CHR$(215);channel #;track #;sector #
THE ORIGINAL BLOCK-READ AND BLOCK-WRITE COMMANDS
Although the BLOCK-READ and BLOCK-WRITE commands are
nearly always replaced by the Ul and U2 commands respectively, the
original commands can still be used, as long as you fully understand
their effects. Unlike Ul and U2, B-R and B-W allow you to read or write
less than a full sector. In the case of B-R, the first byte of the selected
sector is used to set the buffer pointer (see next section), and deter-
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