FORMAT A TRACK
The Format command allows an entire track to be formatted. After a pulse from the IDX pin is detected, the FDC
starts writing data on the disk including gaps, address marks, ID fields, and data fields per the IBM System 34 or 3740
format (MFM or FM respectively). The particular values that will be written to the gap and data field are controlled by
the values programmed into N, SC, GPL, and D which are specified by the host during the command phase. The
data field of the sector is filled with the data byte specified by D. The ID field for each sector is supplied by the host;
that is, four data bytes per sector are needed by the FDC for C, H, R, and N (cylinder, head, sector number and
sector size respectively).
After formatting each sector, the host must send new values for C, H, R and N to the FDC for the next sector on the
track. The R value (sector number) is the only value that must be changed by the host after each sector is formatted.
This allows the disk to be formatted with nonsequential sector addresses (interleaving). This incrementing and
formatting continues for the whole track until the FDC encounters a pulse on the IDX pin again and it terminates the
command. Table 41 contains typical values for gap fields which are dependent upon the size of the sector and the
number of sectors on each track. Actual values can vary due to drive electronics.
Table 40 - FORMAT FIELDS
SYSTEM 34 (DOUBLE DENSITY) FORMAT
DATA
AM
GAP4 SYN IAM GAP SYN IDAM C H S N C GAP SYN
C
R
C
a
C
1
C
2
C
DAT
A
GAP
3
Y D E O R
GAP
4b
80x
4E
12x
00
50x 12x
4E 00
22x 12x
L
C
C
4E
00
3x FC
C2
3x FE
3x FB
A1 F8
A
1
SYSTEM 3740 (SINGLE DENSITY) FORMAT
DATA
AM
GAP4 SYN IAM GAP SYN IDAM C H S N C GAP SYN
C
R
C
a
C
1
C
2
C
DAT
A
GAP
3
Y D E O R
GAP
4b
40x
FF
6x
00
26x
FF
6x
00
11x
FF
6x
00
L
C
C
FC
FE
FB or
F8
PERPENDICULAR FORMAT
DATA
AM
GAP4 SYN IAM GAP SYN IDAM C H S N C GAP SYN
C
R
C
a
80x
4E
C
12x
00
1
C
2
C
DAT
A
GAP
3
Y D E O R
GAP
4b
50x 12x
4E 00
41x 12x
L
C
C
4E
00
3x FC
C2
3x FE
3x FB
A1 F8
A
1
SMSC DS – FDC37N3869
Page 48
Rev. 10/25/2000
SMSC [ SMSC CORPORATION ]
