Data Recording Format; Gap 1; Sync Field - IBM 5280 Maintenance Information Manual

DATA RECORDING FORMAT
G
A
CC G
A
CC
G (
a M
RR
a
M
RR
a )
p
Sync Field 10 Field
CC
p
Sync Field
Data Field or
CC
:
{
Control Field
1
1 2 2
\
Index
Pulse
Occurs
~
Direction of Rotation
Gap 1
This gap separates the index pulse from the sync field of
the first record. In FM format, gap 1 consists of 73 bytes
of hex F F. In M F M format, gap 1 consists of 146 bytes
of hex 4E.
Sync Field
This field synchronizes the diskette control circuitry to the
information being read from the diskette. Each sync field
contains a set number of bytes of hex 00. In FM format,
the sync field contains 6 bytes. In M FM format, this field
contains 12 bytes.
AM 1
AM 1 is the address mark that identifies the following field
as an ID (identification) field. In FM format, this field
contains 1 byte that is always hex FE. In MFM format,
this field contains 4 bytes that are always hex AlA 1 A 1 FE.
10 Field
The I D field is made up of the track address, head address,
record address, and record length.
74 Theory
One Record of a Diskette Track
The track address contains a hex number from 00 through
hex 4A (hex 00
=
track 00, hex 01
=
track 01, hex 02
=
track 02, and so on).
The head address for a diskette 1 is always hex 00. For a
diskette 2 and 2D the head address contains either hex 00
or hex 01.
The record address contains a hex number from hex 01
through hex
1
A (hex 01
=
sector 1, hex 02
=
sector 2,
and so on).
The record length contains a number from 0 through 3
depending on the number of sectors the track is divided
\l
into:
Record Sector Per Record
Number Format Track Length
0
FM
26
128 bytes
FM 15 256 bytes
2 FM
8
512 bytes
MFM
26
256 bytes
2 MFM 15 512 bytes
3 MFM
8
1024 bytes
Note: If any record on a track is damaged, all records on
that ttack wi II have hex F F recorded as the record length.