HP and/or Seiko-Epson IC memory card patent(s)?

[Steve Simpkin]

I looked at the HP Journal editions that covered the HP 48SX (June 1991) and HP 48G/GX (August 1994). While they did describe the memory card interface and other details, they did not mention any patent information that I could find. The closest I was able to find was a comment from compatible memory card manufacturer CMT regarding their use of "tranzorbs" for ESD protection instead of the "patented" shutter used by Epson.

"The transzorb is a high speed transient absorber that is used to help protect
the card's circuitry from transient voltage spikes. The shutter is patented by
EPSON (I believe) so we chose to use tranzorbs for protection against ESD."

The full text is available from:
https://www.hpcalc.org/hp48/docs/misc/cmtcards.txt