IBM 7074 General Information Manual page 15

for
RA.
For example, if
RA
contains ten digits, then 14
BCD
1's must be used. For operation in the eight-bit
mode,
BCD
3' s must be used instead of
BCD
1. There
must be as many record address areas on the format
track as there are records.
Y Gap: A Y gap must follow every
RA.
This gap is
made up of one
BCD
2, followed by 10
BCD
1's and a
BCD
2 for the 6-bit mode of operation. For the 8-bit
mode, the Y gap is made up of one
BCD
4 followed by
10
BCD
3's and another
BCD
4.
Record Areas: There must be four more
BCD
1's than
there are characters in the record, for the 6-bit mode
of operation. For example, for an 80 character record,
84
BCD
1's must be provided. For the 8-bit mode,
BCD
3's are to be used instead of the
BCD
1's. This area
must contain at least six characters, that is, a two
character record plus the four extra
BCD
characters.
Gap 3: Gap 3 is a one character gap that follows
the last record area on the track. This character is
either a
BCD
2 or a
BCD
4, depending upon the mode
of operation.
Format tracks can be written for one mode of opera-
tion or the other, never, as a mixture of both modes,
excepting the track identification area, which is al-
ways written in the 8-bit mode.
Write Home Address Operation
The conditions necessary for this operation are that
the home address switch on the 7631 be on, that a
prepare to verify (home address) operation order be
issued to the file control, and that the write command
immediately follow. The file control compares the
physical address portion of the home address on the
particular track and begins the write operation at
the beginning of the
HA2
area. The first characters
must be the home address identifier of the particular
track. The home address identifier must be a mini-
mum of two characters. If desired, this area may be
extended to match the word length of the using sys-
tem. The number of characters requested by the 7631
for the
HA
identifier is determined by the number of
ones that were previously written on the format. All
characters of the
HA
identifier after the second are
non-significant and will not be a part of address
compare.
This operation continues with the file control detect-
ing the gap between the
HA2
and the first record ad-
dress. On detection of the gap, the file control then
writes the three-digit check character. The operation
continues writing record addresses and records to the
end of the track.
If a stop signal occurs before sensing the end of
track, data transmission stops, but the file control con-
tinues writing blanks to the end of the track.
14
Write Track with Addresses Operation
Conditions necessary for this operation are a prepare
to verify (track with addresses) order, followed by a
write command. Under control of the prepare to verify
(track) order, the file control searches the data track
for a home address and compares this address bit for
bit against the address that was previously issued with
the prepare to verify (track) command. If the home
address fails to compare, the file control issues an im-
mediate
UNUSUAL END
and indicates in its status word
a no record found bit. Upon a successful home address
compare the file control will transfer the record ad-
dress and proceed in the usual manner. The file con-
trol continues filling the record area with data from
the computer. This includes both records and ad-
dresses. The file control also supplies the check char-
acters to be written at the end of each area. When the
last check character area is reached, a
NORMAL END
will be issued to the computer providing no error con-
ditions have been detected. Otherwise,
UNUSUAL END
results. If the computer signals
STOP
in the middle of
a record, data transmission stops, but file control
writes blanks to end of record area, then writes the
check characters.
Write Single Record Operation
Conditions necessary for this operation are that a pre-
pare to verify (single record operation) order be is-
sued to the file control and that a write command fol-
low. The record address area is recognized in the file
control by sensing the end of a long gap in the format.
Upon finding a record address area, the file control
reads off the address contained in the area and com-
pares it bit by bit with the address previously sup-
plied to the adapter during prepare to verify (single
record). If the address does not compare, the file con-
trol continues searching succeeding address areas and
comparing the address contained in each. If the file
control passes the index point twice without com-
paring the address, it will register the no-record-
found status bit and issue an
UNUSUAL END
to the com-
puter without transmission of data. Upon an address
compare true, the file control will cause the 1301 to
write over the record immediately following the com-
pared address. Data are furnished by the system. The
file control· automatically transmits the code check
characters following the end of the record area as
defined by the format track.
If a stop signal is received at a midpoint in the rec-
ord area the file control will continue to write the rec-
ord, with blanks until the end of the formatted area
is reached. After the check characters are recorded,
a
NORMAL END
is issued to the system unless a data
check has occurred, in which case
UNUSUAL END
would
result.