Serial Electrically Erasable Programmable Read-Only Memory Implementation of Personal Computer Memory Card International Association Attribute Memory

Serial Electrically Erasable Programmable Read-Only Memory Implementation
of Personal Computer Memory Card International Association Attribute
Memory

      A method for providing attribute memory for Personal Computer
Memory Card International Association (PCMCIA) cards utilizing a
reprogrammable serial Electrically Erasable Programmable Read-Only
Memory (EEPROM).  The invention is comprised of a Ready/Busy
Circuitry, a Serial Interface Circuitry, Host Interface Circuitry,
Mode Selection Circuitry and a Local Buffer.

      A circuit is disclosed which is capable of ensuring that valid
Attribute memory will be presented by a PCMCIA card to a host PC
system by one of two means.  Attribute memory is a software
architecture element of the PCMCIA standard that requires compliant
PCMCIA cards to provide Card Information Structure (CIS) data to the
host PC in a region of memory called Attribute Memory.  The CIS
contents identify the card and describe the resources it needs from
the host PC to function.  Conceptually this information is ROM, in
that the configuration of the card is not something that is user
updatable, it is instead a fixed characteristic of the card.

      However, situations arise whereby a manufacturer may wish to
alter the contents of the CIS.  For example, a customer wishing to
buy cards for resale may with to customize the contents of the CIS to
reflect their name as manufacturer rather than the original equipment
manufacturer's name.  Similarly, in the manufacturing cycle, updates
to card function or configuration may make it desireable to modify
the
details of the CIS to report these additional capabilities to
systems.

      Typically the CIS contents are provided by a parallel storage
device, namely an embedded mask ROM in an ASIC or an external ROM
module.  Both of these implementations suffer from particular
hazards.  The embedded ROM implementation is not alterable.  The
external ROM implementation is expensive in light of the fact that
typically the CIS size is small (100-200 bytes of data in a multi
kilobyte ROM).  The current embodiment offers a new means for
providing attribute memory above and beyond the two just mentioned.

      Operational Mode 1 --- Serial Access Disabled - The choice as
to which means of providing attribute memory is made by the Mode
Selection Circuitry (MSC).  At the time that the PCMCIA card is
powered up, the Ready/Busy Circuitry (RBC) asserts the BUSY signal to
the PCMCIA enabled host PC in which the PCMCIA card is inserted.

This action ensures that the Host PC will not att...