Commodore 1581 - Chapter 6: Direct Access Commands; Opening Data Channel for Direct Access

BLOCK-READ
The purpose of a BLOCK-READ is to load the contents of a speci
fied sector into a file buffer. Although the BLOCK-READ command (B-
R) is still part of the DOS command set, it is nearly always replaced by
the Ul command (See Chapter 6).
FORMAT FOR THE BLOCK-READ COMMAND:
PRINT#15, "Ul"; 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 num
ber, and "track #" and "sector #" are respectively the track and sector
numbers containing the desired block of data to be read into the file
buffer.
ALTERNATE FORMATS:
PRINT#15,"Ul:"channel #;drive #;track #;sector #
PRINT#15,"UA:"channel #;drive #;track #;sector #
PRINT#15,"Ul:channel #,drive #,track #,sector #"
EXAMPLE:
Here is a complete program to read a sector into disk memory us
ing 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 $1FOO Define a memory buffer.
120 INPUT"TRACK TO READ";T Select a track
130 INPUrSECTOR TO READ";S and sector.
140 OPEN 15,8,15 Open command channel.
150 OPEN 5,8,5,"#" Open direct access channel.
160 PRINT#15,"Ul";5;0;T;S Read sector into disk buffer.
170 FOR I = MB TO MB + 255 Use a loop to
180 GET#5AWF A$ = " " copy disk buffer.
THEN A$ = CHR$(0) into computer memory.
190 POKE IASC(A$) Tidy up after.
200 NEXT
210 CLOSE 5:CLOSE 15
220 END
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