Browse Prior Art Database

Determining the Parity for Setting And Resetting a Register

IP.com Disclosure Number: IPCOM000120502D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 120K

Publishing Venue

IBM

Related People

Kohler, H: AUTHOR [+3]

Abstract

This article describes a method for predicting the parity of a data register after it has been operated on by a SET or a RESET mask contained in a mask register. This method is implemented by counting how many bits in the data register have been changed by corresponding bits in the mask register after completion of the SET or RESET operation. The value obtained is either even or odd and can be used in conjunction with the original parity of the mask register to determine whether the new value in the mask register will have an even or odd parity. If the mask register changes the value of only one bit in the data register, the parity of the data register will be changed, whereas if it changes two bits, the parity of the data register will remain unchanged.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Determining the Parity for Setting And Resetting a Register

      This article describes a method for predicting the parity
of a data register after it has been operated on by a SET or a
RESET mask contained in a mask register.  This method is implemented
by counting how many bits in the data register have been changed by
corresponding bits in the mask register after completion of the SET
or RESET operation.  The value obtained is either even or odd and can
be used in conjunction with the original parity of the mask register
to determine whether the new value in the mask register will have an
even or odd parity.  If the mask register changes the value of only
one bit in the data register, the parity of the data register will be
changed, whereas if it changes two bits, the parity of the data
register will remain unchanged.

      The following examples (Fig. 1) concern parity predictions for
different data patterns (odd parity assumed).  Figs. 2 and 3,
respectively, show this principle for a SET and a RESET of the data
register.

      The number of changing bits in the data register (right-most
column) is the difference between the number of active bits in the
mask register and the number of bits which do not change in the data
register, with the corresponding bits in the mask register being "1".

      Whether the number of bits which do not change, with the
corresponding bits in the mask register being "1", is even or odd is
determined by a bit-by-bit comparison of the mask and the data
register.  Every active bit in the mask register, with the
c...