3. Data Formats
3.6 Parity H/V
17
3.6 Parity H/V
Function and purpose
Parity check provides a mean of checking whether the tape has been correctly perforated or not.
This involves checking for perforated code errors or, in other words, for perforation errors. There
are two types of parity check: Parity H and Parity V.
(1) Parity
H
Parity H checks the number of holes configuring a character and it is done during tape
operation, tape input and sequence number search.
A parity H error is caused in the following cases.
(a) ISO
code
When a code with an odd number of holes in a significant data section has been detected.
(b) EIA
code
When a code with an even number of holes in a significant data section has been
detected.
Parity H error example
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This character causes a parity H error.
When a parity H error occurs, the tape stops following the alarm code.
(2) Parity
V
A parity V check is done during tape operation, tape input and sequence number search when
the I/O PARA #9n15 (n is the unit No.1 to 5) parity V check function is set to "1". It is not done
during memory operation.
A parity V error occurs in the following case: when the number of codes from the first
significant code to the EOB (;) in the significant data section in the vertical direction of the tape
is an odd number, that is, when the number of characters in one block is odd.
When a parity V error is detected, the tape stops at the code following the EOB (;).
(Note 1)
Among the tape codes, there are codes which are counted as characters for parity
and codes which are not counted as such. For details, refer to the "Table of tape
codes" in "3.1 Tape Codes".
(Note 2)
Any space codes which may appear within the section from the initial EOB code to
the address code or "/" code are counted for parity V check.
