FORMAT FIELDS
SYSTEM 34 (DOUBLE DENSITY) FORMAT
DATA
GAP4a SYNC
IAM
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
AM
C
R
C
80x
4E
12x
00
50x
4E
12x
00
22x
4E
12x
00
DATA
DATA
DATA
GAP3 GAP 4b
GAP3 GAP 4b
GAP3 GAP 4b
3x FC
C2
3x FE
A1
3x FB
A1 F8
SYSTEM 3740 (SINGLE DENSITY) FORMAT
DATA
AM
GAP4a SYNC
IAM
FC
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
C
R
C
40x
FF
6x
00
26x
FF
6x
00
11x
FF
6x
00
FE
FB or
F8
PERPENDICULAR FORMAT
DATA
AM
GAP4a SYNC
IAM
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
C
R
C
80x
4E
12x
00
50x
4E
12x
00
41x
4E
12x
00
3x FC
C2
3x FE
A1
3x FB
A1 F8
Table 24 - Typical Values for Formatting
FORMAT SECTOR SIZE
N
00
00
02
03
04
05
...
SC
12
10
08
04
02
01
GPL1
GPL2
09
19
30
87
128
128
512
07
10
18
46
C8
C8
FM
1024
2048
4096
...
FF
FF
5.25"
Drives
256
256
01
01
02
03
04
05
...
12
10
09
04
02
01
0A
20
2A
80
C8
C8
0C
32
50
F0
FF
FF
512*
1024
2048
4096
...
MFM
128
256
512
256
512**
1024
0
1
2
1
2
3
0F
09
05
0F
09
05
07
0F
1B
0E
1B
35
1B
2A
3A
36
54
74
3.5"
FM
Drives
MFM
GPL1 = suggested GPL values in Read and Write commands to avoid splice point
between data field and ID field of contiguous sections.
GPL2 = suggested GPL value in Format A Track command.
*PC/AT values (typical)
**PS/2 values (typical). Applies with 1.0 MB and 2.0 MB drives.
NOTE: All values except sector size are in hex.
CONTROL COMMANDS
Control commands differ from the other commands in that no data transfer takes place. Three commands generate an
interrupt when complete: Read ID, Recalibrate, and Seek. The other control commands do not generate an interrupt.
Read ID
The Read ID command is used to find the present position of the recording heads. The FDC stores the values from the
first ID field it is able to read into its registers. If the FDC does not find an ID address mark on the diskette after the
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