Portable electronic device with memory having data pointers and circuitry for determining whether a next unwritten memory location exist

Claim 1

A portable electronic device having a contactor electronically connecting a host system, comprising: first memory means, having memory locations, for sequentially storing a sequence of data, including current data and next data following the current data in the sequence of data, from the host system at memory locations of the first memory means; second memory means for storing position data representing a memory location of said first memory means; first determining means for determining whether or not data supplied from said host system is a write instruction for said first memory means; means for writing the current data in an unwritten memory location of said first memory means when said first determining means determines the write instruction is supplied from the host system; second determining means for determining whether or not a next unwritten memory location of said first memory means exists when said determining means determines the write instruction is supplied from the host system; means for storing in said second memory means position data representing a location in said first memory means at which the next data to be stored in the sequence of stored data is to be stored when said second determining means determines that the next unwritten memory location exists; means for outputting, after storing the position data in the second memory means, message data indicating that the next unwritten memory location exists; and means for outputting message data indicating that the next unwritten memory location does not exist when said second determining means determines that the next unwritten memory location does not exist.