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Synchronous Memory Refresh Scheme Which Supports Several Refresh Rates Without Jumpers On Cards Or Planars

IP.com Disclosure Number: IPCOM000099420D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Hardell, W: AUTHOR [+2]

Abstract

This invention prevents multiple memory cards from refreshing at the same time, which can cause large current spikes. It also allows each card to adjust its refresh rate independently.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 82% of the total text.

Synchronous Memory Refresh Scheme Which Supports Several Refresh Rates Without Jumpers On Cards Or Planars

       This invention prevents multiple memory cards from
refreshing at the same time, which can cause large current spikes.
It also allows each card to adjust its refresh rate independently.

      This refresh scheme works as follows.  A real-time clock sends
a refresh clock to each memory card approximately every 16 ms.  For
example, if 4 memory cards are used, card 0 is clocked at 0ms, card 1
at 4ms, card 2 at 8ms, card 3 at 12ms, and card 0 again at
16ms, etc.  This clock can be just a 1-cycle pulse.  When a card
receives a refresh pulse or clock, 1, 2, or 4 addresses will be
refreshed, depending on whether 256K, 1MB, or 4MB DRAMs are on the
card.  The number of addresses to be refreshed per clock can be
calculated by the equation:      REFRESHES/CLOCK =
    CLOCK RATE
    RETENTION TIME         ADDRESSES TO REFRESH

      The clock rate should be adjusted to yield a whole number of
refreshes/clock; for example, if 1MB DRAMs are used,
    15.6 us           = 2
    4 ms : 512 addresses
    The figure shows how cards made with 256K, 1MB and 4MB DRAMs can
be mixed in a system with all refreshing at their optimum rate.  Note
that this method ensures that only 1 memory card is refreshed at a
time, which prevents large current spikes associated with multiple
cards refreshing simultaneously.  It accomplishes this...