Browse Prior Art Database

Refreshing Video RAM during Suspend Mode

IP.com Disclosure Number: IPCOM000113812D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Bland, MM: AUTHOR [+6]

Abstract

Disclosed is a method for refreshing Video RAM (VRAM) and system Dynamic RAM (DRAM) during the suspend mode of a device, using the clock signal of the Real Time Clock. While the clock signal of the system clock is used for this purpose during the operational mode of the device, the system clock is shut down during the suspend mode to conserve power. However, to prevent the loss of data, the VRAM and DRAM circuits need to by refreshed during the suspend mode.

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This is the abbreviated version, containing approximately 88% of the total text.

Refreshing Video RAM during Suspend Mode

      Disclosed is a method for refreshing Video RAM (VRAM) and
system Dynamic RAM (DRAM) during the suspend mode of a device, using
the clock signal of the Real Time Clock.  While the clock signal of
the system clock is used for this purpose during the operational mode
of the device, the system clock is shut down during the suspend mode
to conserve power.  However, to prevent the loss of data, the VRAM
and DRAM circuits need to by refreshed during the suspend mode.

      The CAS-before-RAS refresh cycle is used in the suspend mode.
The VRAM refresh rate is, for example, 15.625 microseconds, or 8 ms
per 512 cycles.  Since the period of the clock signal of the
32.758-KHz Real Time Clock, TRTCCLK, is 30.51 microseconds, the VRAM
refresh cycle occurs at each phase of the TRTCCLK signal.

      The Figure shows the refresh timings of the suspend mode.  The
TRTCCLK_DLY signal is generated using delay lines to delay the
TRTCCLK signal by the RAS precharge time, tRP.  The suspend request
input, SUSPREQ, requests the device to be suspended.  The device
responds to this input with the suspend acknowledge signal, SUSPACK.
When a refresh cycle begins while SUSPREQ is active, the device waits
for the refresh cycle to be completed before issuing the SUSPACK
acknowledge signal.  This acknowledgement signal indicates that the
system clock is ready to be shut down.  The VCASn signal is set up
before the VRASn signal, by a time e...