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Search File Reverse - Read Record Forward |
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|  MIL-D-81347C(AS)
Write Tape Mark - The selected MTT shall write a fixed format
3.5.2.4.1.3.3.2.6
Tape Mark. The Tape Mark shall be a special one-frame record with one frame of Longitudinal Parity
using "Even" Lateral Parity. The special one-frame record consists of "0's''in tape tracks A, B, and
C and "l's" in tape tracks 1, 2, 4, and 8. A Status word with External Interrupt shall be sent to the
computer upon completion of the Write Tape Mark function.
Write Tape Mark, XIRG - The selected MTT shall record an Ex-
3.5.2.4.1.3.3.2.7
tended Interrecord Gap of 3-1/2 inches instead of the normal 3/4 inch IRG preceding the normal Write
Tape Mark operation. The Tape Mark which is written is identical to the Write Tape Mark in normal
operation.
3.5.2.4.1.3.3.2.8
Backspace Record - The selected MTT shall move the tape in
the reverse direction to the next IRG (back one record). The tape shall be properly positioned in the
IRG for reading or writing. If the tape was at Load Point when the Back Space instruction was given,
an Illegal Operation shall be generated and noted in the Status word. The Status word with External
Interrupt shall be sent to the computer upon completion of the Back Space function.
3.5.2.4.1.3.3.2.9
Search File Reverse - Read Record Forward - The MTC shall
search the tape in the reverse direction and compare the first word of each record with an Identifier
word, which is transmitted from the computer to the MTC (with the characters in correct order) by a
one word output buffer. When a compare occurs, the *'Found" record is transmitted in the forward
direction to the computer as a Normal Read.
NOTE
In a Forward Search the first word encountered in
each record is the first word of the record. In a
Backward Search the last word encountered in each
record is the first word of the record. (This is the
same word encountered in the Forward Search with
the characters in the same order).
3.5.2.4.1.3.3.2.9.1
Search File Reverse Operation - The function that specified a
Search File Reverse Operation, will be followed by an Identifier word, of 30 bits, which may be any
configuration of bits except that data bits 24 through 27 may not be zero simultaneously. The Search
portion of the Search File Reverse Operation compares the first word of the record with the Identifier
word. If a find is not made, the MTC shall move on to the next record and compare the first word of
that record with the Identifier word. This process will continue until a find is made, an error occurs,
the search is terminated, or a Tape Mark occurs. When a find is made, the MTC shall perform a
Forward Read Tape operation, which shall be the same as a normal Forward Read operation. The
Read operation shall begin with the Identifier word, with the characters in the correct order, then
continue until the end of the record.
Search File Reverse Conditions - Conditions which may occur
3.5.2.4.1.3.3.2.9.2
during a Back Search File function shall be indicated by an External Interrupt. These conditions are
identical to the Search File conditions.
Search File Reverse Termination - If the MTC does not receive
3.5.2.4.1.3.3.2.9.3
the Search word from the computer before it starts searching a record, an Output Timing Error shall
be generated. The Search File Reverse operation shall be terminated whenever a Parity or Timing
Error is generated. A Tape Mark and a "Normal Completion" shall also terminate the Search File
Reverse operation. When the tape motion is stopped due to an error, the tape shall be positioned in
the IRG after the record in which the error occurred.
Backspace File - The selected MTT shall move the tape in the
3.5.2.4.1.3.3.2.10
reverse direction to the Interrecord Gap beyond the next tape mark. At completion a Status word
with Interrupt shall be sent to the computer.
3.5.2.4.1.3.3.2.11
Read Record Reverse - The selected MTT shall read one record
in the reverse direction. Character order within each computer word shall be in the correct order.
At completion a Status word with Interrupt shall be sent to the computer.
103
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