Electronic postage meter having improved security and fault tolerance features

In a microcomputerized postage meter having a microcomputer, a postage printing mechanism coupled to the microcomputer for printing postage in response to instructions from the microcomputer, and input means coupled to the microcomputer for communicating data to the microcomputer, the microcomputer and printing mechanism being located in a secure housing, the improvement comprising:

• first and second independent non-volatile memory means coupled to the microcomputer and located within the secure housing;
• the programmed microcomputer having means for generating a set of accounting information items, the values of which items have an internal arithmetic relationship to one another irrespective of their individual values, means for writing the set of accounting items into each of corresponding pluralities of locations in the first and second non-volatile memory means, means for retrieving the contents of the corresponding pluralities of locations, and means for comparing the contents of the corresponding pluralities of locations;
• non-user-resettable means coupled to the microcomputer for deactivating the meter in response to a disagreement between the contents of the corresponding pluralities of locations, the non-user-resettable means for deactivating the meter being located within the secure housing, and, once set, being beyond control of the microcomputer;
• the non-user-resettable means for deactivating the meter having associated means coupled to the first and second non-volatile memory means for preventing the microcomputer from writing data into either of the first and second non-volatile memory means and associated means coupled to the postage printing mechanism for preventing activation of the postage printing mechanism;
• and
• an alternate communication path coupled to the first and second non-volatile memory means to enable the external retrieval of the contents of the corresponding pluralities of locations independently of the microcomputer to facilitate possible reconstruction of the correct values of the accounting items.

In a microcomputerized postage meter having a microcomputer, a postage printing mechanism coupled to the microcomputer for printing postage in response to instructions from the microcomputer, and input means coupled to the microcomputer for communicating value setting and print initiation signals to the microcomputer, the improvement comprising:

• a non-volatile memory system including first, second, and third non-volatile memory means coupled to the microcomputer, the first, second, and third non-volatile memory means having respective first, second, and third pluralities of locations, at least the first and second non-volatile memory means being independent of one another;
• the programmed microcomputer having
• means for generating a set of accounting information items, the values of which items have an internal arithmetic relationship to one another irrespective of their individual values,
• means for storing the set of accounting information items in corresponding locations of the first and second pluralities of locations,
• means for storing the set of accounting information items in the third plurality of locations,
• means for changing the values of at least two of the items stored in the third plurality of locations in response to a value setting signal from the input means, the values of the items stored in the third plurality of locations including the changed values, maintaining the same internal arithmetic relationship, and
• means for copying the changed values into the first and second pluralities of locations when the postage printing mechanism is activated in response to a print initiation signal from the input means.

In a microcomputerized postage meter having a microcomputer operable according to a program for supervising the printing operation and for generating, maintaining, and verifying accounting information, postage printing means coupled to the microcomputer for printing postage in response to instructions from the microcomputer, and input means coupled to the microcomputer for communicating data to the microcomputer, the improvement comprising:

• first and second independent non-volatile memory means coupled to the microcomputer;
• monostable multivibrator means having a trigger input and an output, the multivibrator means being operable to maintain the multivibrator output at a first logic level for a predetermined time in response to a triggering signal at the trigger input and to allow the multivibrator output to assume a second logic level distinct from the first logic level when the predetermined time elapses without a triggering signal at the trigger input;
• non-user-resettable means coupled to the multivibrator output for deactivating the meter in response to the appearance of the second logic level on the multivibrator output, the non-user-resettable means for deactivating the meter, once set, being beyond control of the microcomputer and operating to prevent the microcomputer from writing data into either of the first and second non-volatile memory means and to prevent activation of the postage printing mechanism;
• and
• means associated with the microcomputer and coupled to the trigger input for repeatedly generating a triggering signal at intervals substantially less than the predetermined time during operation of the meter;
• the programmed microcomputer having means for detecting a failure condition, means for generating a failure code representative of the type of failure, means for suppressing the triggering signal generating means in response to the detection of a failure condition such that the detection of a failure causes the multivibrator output subsequently to assume the second logic level, whereupon the meter becomes deactivated, and means for storing the failure code in the first and second non-volatile memory means prior to the time that the multivibrator output assumes the second logic level.

In a microcomputerized postage meter having a microcomputer, and input means coupled to the microcomputer for generating signals representative of the value of postage to be printed, the improvement comprising:

• a print head including a print element having postage printing indicia formed thereon and being capable of assuming any one of a plurality of serially disposed positions, the print head being capable of assuming a home position in which printing is impossible;
• stepping motor means coupled to the print element, the stepping motor means having a plurality of positions corresponding to the plurality of print element positions;
• motor driving means coupled to the microcomputer for driving the stepping motor means from a first of the plurality of positions to a second serially adjacent one of the plurality of positions;
• position indicator means coupled to the microcomputer for generating and communicating to the microcomputer an electrical signal representative of the position of the stepping motor means;
• print head sensor means coupled to the microcomputer for generating and communicating to the microcomputer an electrical signal respresentative of whether the print head is in its home position;
• means associated with the microcomputer for activating the motor driving means to effect positioning of the print element;
• means associated with the microcomputer and responsive to the position indicator means for determining whether the stepping motor means has moved from the first position to the second position within a predetermined time interval;
• means for suspending operation of the meter in response to a determination that the stepping motor means has not moved from the first position to the second position within the fixed time interval;
• means associated with the microcomputer and responsive to the print head sensor means for determining whether the print head has left its home position prior to completion of the positioning of the print element;
• and
• non-user-resettable means coupled to the microcomputer for deactivating the meter in response to the determination that the print head has left its home position prior to completion of the positioning of the print element.

In a microcomputerized postage meter having a microcomputer, a postage printing mechanism coupled to the microcomputer for printing postage in response to instructions from the microcomputer, and input means coupled to the microcomputer for communicating data to the microcomputer, the microcomputer and the printing mechanism being located in a secure housing, the improvement comprising:

• non-volatile memory means coupled to the microcomputer, including a plurality of memory locations for storing a set of accounting information items;
• bistable multivibrator means including self-contained power supply means and having an output capable of assuming first and second distinct logic levels in response to first and second respective states of the bistable multivibrator means, the bistable multivibrator means, once in the second state, being beyond the control of the microcomputer and being resettable to the first state only by physical access to the interior of the secure housing;
• means associated with the microcomputer for detecting a failure condition;
• means associated with the microcomputer and coupled to the bistable multivibrator means for causing the bistable multivibrator means to assume its second state in response to the detection of a failure condition;
• power surveillance means for generating a power loss signal in response to a low power condition;
• means responsive to the power loss signal for generating a system clear signal;
• means responsive to the system clear signal for preventing the microcomputer from writing data into the non-volatile memory means;
• means responsive to the system clear signal for preventing activation of the printing mechanism;
• and
• means responsive to the logic level of the bistable multivibrator output for maintaining the system clear signal active in response to the appearance of the second logic level regardless of the state of the power loss signal.