Security system for use with electronic postage meter to prevent lock

Abstract

An electronically operated postage meter includes a non-volatile memory for the permanent storage of security and financial data utilized in the operation of the meter. In the operation of the memory, a standardized two-bit control signal is employed for providing read, write and word-erase commands in addition to one further command, namely, a block-erase command, wherein the entire memory is cleared. To avoid unintentional erasure of the entirety of the stored data, as might occur in the event of a fault in a control circuit or computation circuit coupled to the memory, a control-line translation unit is coupled within a control line which connects a memory control circuit with the memory. The control-line translation unit comprises a logic gate and a feed forward path, the gate operation being transparent to three out of the total of four control signals. Thereby, only the block-erase signal is translated, or converted, to a harmless one of the other control signals, more particularly, to the read signal. Thereby, a block-erase signal does not occur inadvertently due to a failure in a control unit external to the non-volatile memory.