Browse Prior Art Database

Method for Extending a Card Detect and ID Mechanism

IP.com Disclosure Number: IPCOM000121652D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 4 page(s) / 136K

Publishing Venue

IBM

Related People

Downes, RW: AUTHOR [+6]

Abstract

Disclosed is a method for increasing the number of card slots and corresponding IDs that may be interrogated in a card slot query system.

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

Method for Extending a Card Detect and ID Mechanism

      Disclosed is a method for increasing the number of card
slots and corresponding IDs that may be interrogated in a card slot
query system.

      A conventional mechanism consists of a unique signal connected
to each card slot for querying that slot, a dedicated ID Bus for
receiving the card IDs, and a slot table for associating the card IDs
received with the corresponding card slots.  Such a mechanism is more
completely described in the reference [*].  In the conventional
mechanism, the range of possible ID values is a function of the
number of signals in the ID Bus.  For an ID Bus with eight signals,
this provided a range of ID values from 0 to 255.

      Specifically, the card defect and ID (CDID) mechanism consists
of a set of individual ID interrogation signals: "CDID Select(n),"
wired from a "CDID Controller" function to each card slot, and an
8-bit "ID-Bus" shared by each of the slots.  This bus is used to
transport the 8-bit ID code (also termed "CDID" code) from each slot,
when its corresponding "CDID Select(n)" signal is activated.  Cards
are designed to respond to the activation of a slot "CDID Select(n)"
signal with a nonzero 8-bit code. This code is chosen to be unique to
each card type.  Empty slots result in an 8-bit code of zero being
produced.

      Because the CDID mechanism is an integral part of the system
maintenance and service function, the reliability of the above
implementation is extremely important.  This is achieved in the
conventional mechanism by requiring only a single 74LS240, or
equivalent part, be included on each system card.  Correspondingly,
to extend this mechanism to provide additional CDID codes, it was
necessary to satisfy requirements of 1) compatibility with the
conventional mechanism, 2) simplicity, 3) high reliability, and 4)
low cost.  Schematically, the extended CDID mechanism is implemented
as indicated in card slot (x) of Fig. 1.  The conventional mechanism
is implemented as indicated in card slot (y).

      The essential hardware addition to extend the CDID is a simple
state machine (State Mach), as shown in card slot (x) above.  This
state machine has the following minimum characteristics:
      o    It has at least three distinct states.
      o    State changes occur as a result of the "CDID Select(n)"
signal being activated.
      o    At least one of the states is a "null" state in that the
LS240, or equivalent, generates a zero (or some other unique
"reserved" value) CDID code on the "ID-Bus" when this state occurs
and the "CDID Select(n)" signal is active.
      o    At least two or more consecutively occurring states are
"ID code" states in that the LS240, or equivalent, generates nonzero
(or "unreserved" value) CDID codes on the "ID-Bus" when these states
occur and the "CD Select(n)" signal is active.
      o    All remaining states (i.e., states other t...