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Data Check
In a data check, the parity of th§ data, except recognized
EOR characters and delete characters, can be checked if the
parity switch is set to the odd or even position. Regardless
of the tape code used, the data sent from the 2822 to the
channel has odd parity.
TAPE CODE TRANSLATION
The 2671 is capable of reading any tape code that can be
punched in 5-, 6-, 7-, or 8-track tape. (Feed holes alone are
ignored.) This is possible because the translation of the
code punched in the tape is done by System/360. The eight
tracks of the 2671 are connected to the system I/O channel
by bus-in lines as follows:
t r a c k Number
8 7 6 5 4 3 2 1 Odd Parity
l l l l l l l l l
Bus-In Line
0
1 2 3 4 5 6 7 P
When the width of the tape is such that a track does not
exist, a 0-bit is transmitted for that track position.
The eight bus-in lines connect to the eight bits of a core-
storage byte in the System/360 as follows:
Bus-In Lines
Core Storage
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
A hole punched in a track of paper tape is represented as
a 1-bit in its respective position of core storage. A blank in
a track of paper tape is represented as a 0-bit in its
respective position of core storage.
The translate instruction in the System/360 may be used
to convert the tape code to the desired internal code. The
translate instruction operates by adding the binary value
represented by the tape code to the starting address of a
table. The sum of these two numbers is the address of a
position in the table that contains the desired internal
extended binary-coded-decimal interchange code (EBCDIC)
or United States of America standard code for information
interchange (USASCII) code for the character. The internal
code is automatically taken from the table to replace the
tape code in the read-in area.
Special Tape Code Characters
End-of-Record Character
The EOR character is chosen by the customer from among
the spare codes of the tape code. The end-of-record
switches on the 2671 console allow the customer to gener-
ate the coding of the chosen EOR character.
The state of the end-of-record switches is continuously
compared with each character read by the 2671.
If the 2671 is operating under the control of modified
-»read commands, the 2671 stops at each EOR character.
None of the EOR characters is transmitted to the channel.
If the 2671 is operating under the control of unmodified
read commands, the 2671 stops only when the channel con-
trol word count reaches zero. EOR characters up to this
point are transmitted to the channel and are counted as
data characters.
The one condition, however, where an EOR character is
transmitted to System/360 under a modified read com-
mand is as follows:
System/360 program changes from an unmodified read
command to a modified read command, and the first
character of the new record is an EOR character.
The EOR character is not parity checked.
If the EOR character is used to indicate the ends of a
series of fixed-length records, it is advisable to issue succes-
sive modified read commands, rather than unmodified read
commands that are followed by one modified read com-
mand. This enables the translation program to take place at
the end of each record, rather than at the end of the com-
plete tape.
Delete Character
The delete character is that character having all possible
tracks punched. The delete character has this format for all
5-, 6-, 7-, and 8-track codes.
If a mistake in the punching of a character is made, the
bad character is erased by punching all remaining tracks.
The delete character is automatically suppressed in the
2671 provided that the delete switch has been pushed up.
The 2671 does not stop, and the character count in the
channel is unaffected. The delete character is not parity
checked.
NORMAL STOP CONDITIONS
Character Count Equals Zero or EOR Character
After a 2671 operation has been completed, the stop signal
comes either from the system (when the character count
equals zero) or from the detection of an EOR character.
The ready lamp remains on. No operator intervention is
required except when the stop pushbutton was previously
operated. If the stop pushbutton was operated during the
read operation, the ready lamp turns off, and the start
pushbutton must be operated to resume the read operation.
Character Count Equals Zero
When the 2671 is stopped by the System/360 because the
character count equals zero, the third character of the next
record is located at the reading head, the second character
in the buffer, and the first character in the data register.
The first character is ready to be transferred when a new
read operation is initiated by the System/360.
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