Commodore 1541-II - Block-Write

EXAMPLE:
Here is a complete program to read a sector into disk memory using Ul, and from
there into computer memory via Get#. (If a carriage return will appear at least once in
every 88 characters of data, Input# may be used in place of Get#).
110
MB = 7936:REM $1FOO Define a memory buffer
120 INPUT"TRACK TO READ";T Select a track
130 INPUT-SECTOR TO READ";S and sector
140 OPEN 15,8,15 Open command channel
150 OPEN 5,8,5,"#" Open direct access channel
160 PRINT#15,"Ul";5;0;T;S Read sector into disk buffer
170 FOR I = MB TO MB + 255 Use a loop to
180 GET#5,A$:IF A$ = " " copy disk buffer
THEN A$ = CHR$(0) into computer memory
190 POKE I,ASC(A$) Tidy up after
200 NEXT
210 CLOSE 5:CLOSE 15
220 END
As the loop progresses, the contents of the specified track and sector are copied into
computer memory, beginning at the address set by variable MB in line 160, and may be
examined and altered there. This is the basis for programs like "DISPLAY T & S" on the
Test/Demo diskette.
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 block1
will be read was opened; "drive #" is the drive number (always 0 on the 1541); 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,'4U2:''channel #;drive #;track #;sector #
PRINT#15,"UB:"channel #;drive #;track #;sector #
PRINT#15,"U2:channel #,drive #,track #,sector #"
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