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8272
•
Head
Unload Time Interval
•
10
Information when the processor terminates com-
mand
(see
Table
2)
• Definition of
DTL
when N = 0 and when N#-O
I
n the Write Data mode, data transfers between the proc-
essor
and
FDC
must occur every
31
I's in the
FM
mode,
and every
15
I's in the MFM mode. If the time interval
between data transfers
Is longer than this then the
FDC
sets the
OR
(Over
Run)
flag
In
Status Register 1 to a 1
(high),
and
terminates the Write Data Command.
WRITE
DELETED
DATA
This command is the same
as
the Write Data Command
except a Deleted Data Address Mark is written
at
the
beginning of the Data Field instead of the normal Data
Address Mark.
READ
DELETED
DATA
This command is the same
as
the
Read
Data Command
except that when the
FDC
detects a Data Address Mark
at the beginning of a Data Field
(and
SK
= 0
(low)),
It will
read
all the data in the sector and set the
CM
flag
in
Status Register 2
to
a 1 (high),
and
then terminate the
command.
If
SK
=
1,
then the
FDC
skips the sector with
the Data Address Mark and reads the next sector.
READ
A TRACK
This command is similar to
READ
DATA
Command
except that the entire data field is
read
continuously
from each of the sectors of a track.
Immediately after
encountering the
INDEX HOLE, the
FDC
starts reading
all data fields on the track
as
continuous blocks of data.
If the
FDC
finds
an
error
in
the
10
or
DATA
CRC
check
bytes, it continues to
read
data from the track.
The
FDC
compares the
10
information
read
from each sector with
the value stored
In
the
lOR,
and sets the
NO
flag of
Status Register 1 to a 1 (high)
If there is no comparison.
Multi-track or skip operations are not allowed with this
command.
This command terminates when
EOT
number of sectors
have
been
read.
If the
FDC
does not find
an
10
Address
Mark
on
the diskette after it encounters the INDEX
HOLE
for the second time, then it sets the MA (missing
address
mark)
flag in Status Register 1 to a 1 (high), and
terminates the command. (Status Register
0 has bits 7
and
6 set to 0
and
1 respectively.)
READID
The
READ
10
Command is used
to
give the present posi-
tion
of
the recording
head.
The
FDC
stores the values
from the first
10
Field it is able to read. If no proper
10
Address Mark is found
on
the diskette, before the
IN-
DEX
HOLE is encountered for the second time then the
MA
(Missing Address
Mark)
flag in Status Register 1 Is
set to a 1 (high), and
if
no data Is found then the
NO
(No
Data)
flag Is also set
in
Status Register 1 to a 1 (high)
and the command is terminated.
FORMAT A
TRACK
The Format Command allows
an
entire track to
be
for-
matted. After the
INDEX
HOLE
Is
detected, Data is writ-
ten on the Diskette: Gaps, Address Marks,
10
Fields and
Data Fields, all per the
IBM System
34
(Double Density)
or System
3740
(Single Density) Format are recorded.
The particular format which will
be
written Is controlled
by the values programmed into N (number of bytes/sec-
tor),
SC
(sectors/cylinder),
GPL
(Gap
Length), and 0
(Data Pattern) which
are
supplied by the processor dur-
ing the Command Phase. The Data Field Is filled with
the Byte
of
data stored in
D.
The
10
Field for each sector
is supplied
by
the processor; that is, four data requests
per sector are made by the
FDC
for C (Cylinder Number),
H (Head Number), R (Sector Number) and N (Number of
Bytes/Sector). This allows the diskette to
be
formatted
with nonsequential sector numbers,
if
desired.
After formatting each sector, the processor must send
new values for
C,
H,
R,
and N to the
8272
for each sector
on the track.
The
contents of the R register is
In-
cremented
by
one after each sector is formatted, thus,
the R register contains a value of R
+ 1 when It Is
read
during the Result
Phase.
This incrementing and format-
ting continues for the whole track until the
FDC
en-
counters the INDEX
HOLE
for the second time, where-
upon it terminates the command.
If a FAULT signal is received from the FDD at the end of
a write operation, then the
FDC
sets the
EC
flag of
Status Register
0 to a 1 (high), and terminates the com-
mand after setting bits 7 and 6 of Status Register 0 to 0
and 1 respectively. Also the loss of a
READY
signal at
the beginning of a command execution phase causes
command termination.
Table 5 shows the relationship between
N,
SC,
and GPL
for various sector sizes:
TABLE
5.
SECTOR SIZE RELATIONSHIPS
FORMAT
SECTOR
SIZE N
SC
GPL
'
GPL
2
REMARKS
128
bytes/Sector
00
1
,,-{16)
07(16)
18(16)
IBM Diskette 1
FM Mode
256
01
OF(16)
OE(16)
2A(16)
IBM Diskette 2
512
02
06
1B(16)
3,,-{16)
1024 bytes/Sector
03
04
-
-
FM Mode
2046
04
02
- -
4096
05
01
-
-
256
01
1A(16)
O~16)
36(16)
IBM Diskette
20
512
02
OF(16)
1B(16)
54(16)
MFM Mode
1024
03
06
35(16)
74(16)
IBM Diskette
20
2048
04
04
-
-
4096
05 02
-
-
8192
08
01
- -
Note:
1.
Suggested
val~es
of GPL in
Read
or Write Commands to avoid splice point
between data
field
and
10
field of contiguous sections.
2.
Suggested values
of
GPL
in
format command,
9-59