Records
Format Records
The
format records are located on channel 0
of
the
tape. The first
251
bytes
of
a record are hex 55; they
are used
as
a
start/stop
zone
for
the tape unit. The
next three bytes are used
to
provide position and timing
information
to
the controller. The first
two
of
these
three bytes are hex
00; they are read, one
bit
at a time,
until the third byte, hex
E7,
is read.
~
Forward
Tape
Motion
Format
Record
I
I
Format
Record
At
this point, the tape unit and the processor are
synchronized, and the tape adapter switches
to
byte
mode.
The next
byte
is the record type;
it
indicates
to
the
controller whether the data track has a header record by
a data record written on it. Following this byte is the
record sequence byte;
it
identifies the riext record on
the data track. The next 29 bytes
of
hex
00
provide a
time delay that is used between erasing the data track
of
one record and writing the data track
of
the next
record. The last four bytes
of
the format track are used
to
establish synchronization and
to
determine the record
type
if
the tape unit is reading
in.
the reverse direction.
Format
Record
Last
Data
I
........................
Header
Record
............
Data
Record
Data
Record
Number 2
Record
in
Previous
File
No
Data
I
I
I
I
I
I
I
I
251
Bytes
of
Hex
55
..................
Number 1
............
................
R ecor
dT
ype
....................................
~
I~
I~
I
'I
I
29
Bytes
of
Hex
00
'-,,-'.
Record
Sequence
Number
............
......
E
0
7 0
.......
-
0
0
I
No
Data
r-----
Record
Type)
-----
....
Format Record
) Record Type:
4-34
Header
-
Hex
81
Data
-
Hex
18
o 0 No
7 0 0
Data
File Number Number
of
Bytes Allocated
to
File
Hex
0001·7FFF
--
....
1
r-
Hex
0001·3FFF
.--"'--...
--..
Language
Dependent Information
File Type
/
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