Browse Prior Art Database

Using Diodes to Reduce Pins/Signals Needed to Access Memory SIMM Presence Detect Codes

IP.com Disclosure Number: IPCOM000111810D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Hardell Jr, WR: AUTHOR

Abstract

This disclosure provides a means to reduce pins/signals needed to access memory SIMM presence detect codes. This will allow dotting of different memory SIMM presence detect (PD) lines on the memory card or planar. The diodes allow the dotting to be done with passive devices that require little board space and no power when inactive.

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Using Diodes to Reduce Pins/Signals Needed to Access Memory SIMM
Presence Detect Codes

      This disclosure provides a means to reduce pins/signals needed
to access memory SIMM presence detect codes.  This will allow dotting
of different memory SIMM presence detect (PD) lines on the memory
card or planar.  The diodes allow the dotting to be done with passive
devices that require little board space and no power when inactive.

      Presently, memory SIMMs (Fig. 1) contain Presence Detect (PD)
codes.  The PD code pins are either open or shorted to ground on the
SIMM.  The PD code lines on the planar (or memory card) have
individual pullup resistors.  When the SIMM is plugged in, it will
short the appropriate PD lines to ground.  The PD codes can be used
to indicate the size, speed (access time), and other characteristics
of the SIMM.  All lines high (no shorts to ground) can be used to
indicate that no SIMM is plugged in.

      This is a method of reducing the number of pins/signals needed
to access the PD codes on memory SIMMs.  First, the PD lines of
multiple SIMMs are dotted on the planar (Fig. 2).  For a memory card
with 16 SIMMs and 6 bits per SIMM, this will reduce the number of
lines from 16*6=96 to 6+16=22 (6 PD lines+16 enable lines).  Now, the
shorts to ground are replaced with diodes (1 diode per PD line).  One
side of each diode is connected to a PD line that will be pulled low.
The other side of the diodes will connected to an enable sig...