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Shadow Latches for Synchronized Reading of Error Registers

IP.com Disclosure Number: IPCOM000101313D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Hardell, WR, Jr: AUTHOR [+3]

Abstract

Disclosed is a means to read related registers while keeping the data from the registers in sync with each other. In this method there is a shadow latch for each of the related registers except one. The register without a shadow latch must be read first. When the register without a shadow latch is read, the other registers are stored in the shadow latches.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Shadow Latches for Synchronized Reading of Error Registers

       Disclosed is a means to read related registers while
keeping the data from the registers in sync with each other.  In this
method there is a shadow latch for each of the related registers
except one.  The register without a shadow latch must be read first.
When the register without a shadow latch is read, the other registers
are stored in the shadow latches.

      Consider a system with two error registers that need to be
synchronized with each other (see Figure 1).  For this example,
assume that there are two related error registers: the error status
and the error address.  If the status is read on one cycle and the
address is read on a later cycle, then the address might have changed
by the time it is read (if an additional error occurs between the
reading of the status and address).  To make sure that the address
that is read matches the status that is read, a shadow latch is used
for the address register.

      Figure 2 shows the configuration for three registers. In this
example, register 1 would be read first.  Registers 2 and 3 would be
stored in the shadow latches on the same cycle that register 1 is
read.  Then registers 2 and 3 can be read later from the shadow
latches.