Postage meters are mass produced devices for printing a defined unit value for governmental or private carrier delivery of parcels and envelopes. The term postage meter also includes other like devices which provide unit value printing such as tax stamp meters. Postage meters include internal accounting devices which account for postage value representation which is stored within the meter. The accounting device accounts for both the recharging of the meter with additional postage value and the printing of postage by the meter printing mechanism. No external independent accounting system is available for accounting for the postage printed by the meter. Accordingly, postage meters must possess a high reliability to avoid the loss of user or governmental funds stored within the meter and dispensed by printing postage.
Electronic postage meters have been developed and are disclosed, for example, in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM; in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS; and, in European Patent Application, publication No. 0 019 515, for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES. Such meters have electronic accounting circuits which include electronic non-volatile memory capability for storing postage accounting information. The accounting circuits and associated postage printing mechanism are physically sealed within a tamper resistant enclosure. The non-volatile memories are provided for storing critical postage accounting information when external operating power is not applied to the meter.
Various types of accounting information may be stored in the meter non-volatile memory. This information includes, for example, the total amount of postage remaining in the meter for subsequent printing (descending register) and the total amount of postage printed by the meter (ascending register). Other types of accounting or operating data may also be stored. For example, service information in the form of error codes denoting various types of malfunctions or abnormal conditions encountered during operation of the meter may be stored in non-volatile memories. This facilitates the evaluation of the operating experience of each meter to assist in its repair, should that be necessary, and to accumulate data helpful in the design of electronic postage meters.
Non-volatile memories as well as the other electronic accounting circuitry within electronic postage meters are susceptible to disturbances which can either destroy information or cause erroneous information to be generated. The electronic circuits are susceptible to electromagnetic radiation and electrical transients which can interfere with the proper operation of the meter and accurate storage of information. These types of effects can result in a loss of funds to the users and, accordingly, it has been recognized that various types of protection must be provided to avoid such undesirable results as the data cannot be reconstructed in most instances from other externally available records.
One type of sequence of operation when a malfunction is detected can include locking the meter against continued operation. In such case, a meter shutter bar may be positioned to prevent further operation of the printing mechanism and an interposed moved into a position to lock the shutter bar in its blocking position. When this occurs, the meter becomes inoperable to print further postage. Additionally, under certain failure or malfunction conditions, the non-volatile memories may not be accessible by the keyboard actuation. An example of such a malfunction would include a failure of the microprocessor in the meter or necessary peripheral circuits such as, depending upon the design, system clocks and memory address decoders. Systems such as that disclosed in the above-noted European Patent Application have also been designed to intentionally limit access to non-volatile memory when certain failure conditions are detected.
When the meter malfunctions and is taken out of service, it is necessary to determine the remaining balance of postal funds stored within the meter non-volatile memory and available for printing (descending register) so that such amount can be refunded to the customer or user. Depending on the type of meter usage and the point in time when a malfunction occurs, many thousands of dollars of postage may be stored in the non-volatile memory descending register. However, before a refund can be made to the user or customer, it is necessary to read out the contents of the non-volatile memory. This is not possible in systems where access to the non-volatile memory stored data requires utilization of the meter microprocessor or peripheral memory circuits, should these be inoperative. In this case, the meter housing must be opened and the meter memory physically accessed before proper amount of funds to be refunded can be determined.
In the electronic postage meter system described in the above-noted European Patent Application, when the meter becomes inoperable due to a fault condition, the non-volatile memories are accessible by an external channel connected from outside of the sealing housing. Once the meter has been set to a faulted state, the non-volatile memory contents can be read out independently of the meter microprocessor and the microprocessor is prevented from accessing the non-volatile memory. Necessary power to read the non-volatile memory is supplied to the memories through the external channel to enable reading of the non-volatile memory contents through the external channel without supplying power to the microprocessor.
Another system for reading the contents of the non-volatile memory when an electronic postage meter is inoperative is disclosed in U.S. patent application Ser. No. 344,651 filed Feb. 1, 1982, for ELECTRONIC POSTAGE METER HAVING POWER MAGNETICALLY COUPLED TO THE METER FROM THE METER BASE, now U.S. Pat. No. 4,471,440. The system includes having a plurality of locations for storing the postage accounting data in predetermined locations of a non-volatile memory which are physically accessible when the memory is removed from the meter. The locations are chosen so that they can be scanned by a scanning device to determine the orientations of the bit patterns without energizing the non-volatile memory and without physically altering the non-volatile memory structure.
Still another system for accessing electronic postage meter non-volatile memories when the meter is inoperative is described in U.S. patent application Ser. No. 399,594 filed July 19, 1982, for ACCESSIBLE HOUSING FOR ELECTRONIC SYSTEM, now U.S. Pat. No. 4,507,744. In this application, an auxiliary communication channel is provided containing read access lines to the non-volatile memory. Access to this communication channel is provided through a sealed access door, which provides both evidence of tampering when opened and electromagnetic interference protection when sealed. The access door is designed for operation on a single occasion only. Access through the door precludes further normal meter operation by deactivating the meter in such a manner that reactivation is not possible without disassembling of the meter housing which will result in evidence of tampering. Thus, the customer has immediate access to the postage funds upon reading the memory contents while achieving protection of the data, prevention of unauthorized alteration of the postage funds balance and unauthorized use of the meter.