Commodore Plus 4 - Page 348

336 Using Peripheral Devices
Direct-access programming requires opening two channels to the disk drive.
The first is the command channel, which is opened with
OPEN fUenumber,device,lB
where Jilenumber is the logical file number to associate with the command
channel and device is the disk drive's device number. The second is a direct-access
channel, which is opened with
OPEN fUenumber,deviGe,chajmei;'#bu£fei/'
where filenumber is the logical file number to associate with the direct-access
channel, device is the disk drive's device number, and channel is a data channel to
use for direct access (2-14). The 1541 has several internal buffers. Four of these
are used for direct-access programming. You need not specify which one to use.
Alternatively, you may do so by using buffer equal to 0 through 3. The 1541
memory corresponding to each buffer is as follows:
Buffer 1541 Memory Used
0 $0300-$03FF
1 $0400-$04FF
2 $0500-$05FF
3 $0600-$06FF
Each channel opened must be closed, following its use, with
CLOSE filenumber
The diskette is organized into tracks and sectors. There are 35 tracks, num
bered 1 to 35, on a 1541 format diskette. The number of sectors within a track
varies according to the following:
Tracks Number of Sectors
1-17
18-24
25-30
31-35
21
19
18
17
The sectors are numbered starting with zero. Hence, for example, the sectors on
track 1 are numbered 0-20.