ELECTRONIC POSTAGE METERSYSTEM

Abstract: A memory protection circuit for a postage meter pre­ vents the inadvertent writing of spurious data into memory locations in nonvolatile memory (62) during a power down cycle. The memory protection circuit works in conjunction with a WRITE voltage terminal associated with the nonvola­ tile memory (62). Means (100, 64) couple a first voltage source (78, 82, 84, 86, 88) providing a predetermined polarity voltage to the WRITE voltage terminal when a predetermined power condition exists such that the nonvolatile memory (62) is enabled to have data written into memory locations thereof. When the predetermined power condition does not exist, the means (100, 64) utilize a second different voltage source (66, 68, 72) to change the voltage level at the WRITE voltage terminal to ensure that data is not written into the memory locations.

Description: The present invention relates to an electronic postage meter system. Electronic postage meter systems have been developed as for example the systems disclosed in US-A-3,978,457 for Microcomputerized Electronic Postage Meter Systems, in US-A-3,938,095 for Computer Responsive Postage Meter and in EP-A-19515, for Electronic Postage Meter Having Improved Security and Fault Tolerance Features. Electronic postage meters have also been developed employing plural computing systems. Such a system is shown in US-A-4,301,507, for Electronic Postage Meter Having Plural Computing Systems and assigned to Pitney Bowes Inc. The accounting circuits of electronic postage meters include nonvolatile memory capability for storing postage accounting information. This information includes, for example, the amount of postage remaining in the meter for subsequent printing or the total amount of postage printed by the meter. Other types of accounting or operating data may also be stored in the nonvolatile memory. The memory function in the electronic accounting circuits have replaced the function performed in previous mechanical-type postage meters by mechanical accounting registers. Postage meters with mechanical accounting registers are not subject to the many problems encountered by electronic postage meters. Conditions cannot normally occur in mechanical-type postage meters that prevent the accounting for a printing cylce or which result in the loss of data stored in the registers. Moreover, in mechanical postage meters it is not necessary electronically to monitor the position of the mechanical components associated with printing postage. This, howver, is not the case with electronic postage meters. Conditions can occur in electronic postage meters where information stored in electronic accounting circuits can be permanently lost. Conditions such as a total line power failure or fluctuation in voltage conditions can cause the microprocessor associated with the meter to operate erratically and either cause a loss of data or the storage of spurious data in the nonvolatile memory. The loss of data or the storage of spurious data may result in a loss of information representing the postage funds stored in the meter. Since data of this type changes with the printing of postage and is not stored elsewhere outside of the meter, there is no way to recover or reconstruct the lost information. In such a situation, a user may suffer a loss of postage funds. To minimize the likelihood of a loss of information stored in the electronic accounting circuit, efforts have been expended to ensure the high reliability of electronic postage meters. Some systems for protecting the critical information stored in the meter are disclosed in the above-noted patents and applications. EP-A-19515 discloses an electronic postage meter employing a microprocessor and dual redundant battery-backed CMOS memories to store critical meter data. The write control lines of the memories are jointly controlled by an output line of the microprocessor and by a voltage sensing circuit in order to prevent writing to the memories during power up and power down conditions. An additional arrangement to protect the postage meter accounting information is shown in US-A-4,285,050 (GB-A-2062311) for Electronic Postage Meter Operating Voltage Variation Sensing System. This arrangement has the features in the 1st portion of claim 1. In this arrangement the MNOS (metall-nitride-oxide-silicon)-memory device is enabled for writing by applying a -30V DC potential at a write-control line of the memory and the memory is disabled for writing by only removing this potential. Electronic design News, Vol. 23, No. 7,5,4. 1978, pp 120-122 suggests applying a logic ONE to the CE input to avoid destroying or modifying memory contents during a power down cycle. No attempt is made in the system described in this document to transfer data from a volatile memory to a non-volatile memory as in GB-A-2062311. Furthermore, the application of the logic ONE to the CE input clearly operates in accordance with outputs generated by the 16 bit microprocessor, thus not being independent of microprocessor operation. It has been recognized that it is desirable to keep the power supply for electronic postage meters physically associated with and part of the meter. In the event of an external power failure, the power supply within the secure housing of the postage meter continues to generate a sufficient, regulated power, for sufficient time for orderly and accurate transfer of critical information from volatile memory to nonvolatile memory. The problem of ensuring proper power during a power down cycle is compounded because certain nonvolatile memories need several different voltages for proper operation. As an example, one type of solid state nonvolatile memory requires the presence of three different voltages for a WRITE operation. It has been discovered that while microprocessors used in electronic postage meters may be designed to turn off and become inoperative below a predetermined voltage level, such microprocessors may become active again at even lower voltage levels. The microprocessors may turn off below a predetermined voltage level and thereafter within a lower range turn on again and be capable of outputting data. The microprocessors will again turn off below the lower predetermined range. Because of this unreliable operation at turn off, the accounting information within the postage meter can be destroyed by the inadvertent writing of spurious data during a power down cycle when the microprocessor is believed to be inoperative. Moreover, the cost of carefully testing and selecting microprocessor components for postage meters to avoid this problem can greatly increase the cost of such parts, both because of the cost of testing and because of the rejection of the microprocessor devices that exhibit this characteristic. The object of the present invention is to provide an improved electronic postage meter system in which in advertent writing of spurious data into the memory during power-down cycles is substantially overcome. This object is achieved by an electronic postage meter system as defined in claim 1. A better understanding of the present invention may be obtained from the following detailed description of a preferred, exemplary embodiment thereof, making reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram, partly in block form, of an electronic postage meter power supply system according to the present invention; Figures 2 and 3 are alternative embodiments of the invention shown in Figure 1 involving modification of the memory protection circuit; and Figure 4 is a perspective view of an electronic postage meter showing the outer housing, the meter keyboard and meter display. Referring first to Figure 1, a postage meter 12 includes: an accounting module 14 having a microprocessor and nonvolatile memory such as a General Instrument Corporation ER3400 type electronically alterable read only memory (this device is described in a General Instrument Corporation manual dated November 1977, entitled EAROM and designated by number 12-11775-1); a printing module 16 having microprocessor and motor control circuits; and a control module 18 having microprocessor and control circuits. The details of construction and operation of the system may be in accordance with the postage meter systems and the mechanical apparatus shown in the above-noted patent application for Electronic Postage Meter Having Plural Computing Systems and in US-A-4,287,825 for Printing Control System. Postage meter 12 includes a series of opto-interrupters 20, 22, 24, 26, and 28. The opto-interrupters are used to sense the mechanical position of the parts of the meter. For example, the opto-interrupters can be employed to sense the position of a shutter bar which is used to inhibit operation of the meter under certain circumstances, the position of digit wheels of a printer, the home position of a print drum, the position of a bank selector for the print wheels, the position of an interposer, or any other movable mechanical component within the meter. These opto-interrupters are coupled to the printing module 16 which monitors and controls the position of the mechanical components of the meter. The printing module 16 is connected to the accounting module 14 via a serial data bus 30 and communicates by means of an echoplex technique described in the abovenoted U.S. Patent Application for Electronic Postage Meter Having Plural Computing Systems. Both ends of the bus are buffered by an optics buffer, not shown, which is energized by the power supply +5 volt line to be hereafter described. Similarly, the control module 18 is connected to the accounting module 14 via a serial data bus 32 and also communicates by means of the echoplex technique. Optics buffers, not shown, are provided to buffer the bus. It should be recognized that the particular architecture of the postage meter system is not critical to the present invention. Plural or single microprocessor arrangement may each be employed with the present invention. A source of operating voltage, such as 110 volt 60 cycle supply, is applied across the meter input terminals 34. The voltage is applied to a linear 10.8 volt power supply 36. The output from the 10.8 volt linear power supply 36 is supplied to a first 8 volt linear regulated power supply 38 and to a second 5 volt linear regulated power supply 40. The 8 volt supply is used to power a display 42 which is operatively coupled via a bus 44 to the control module 18. The output from the power supply 40 is directly coupled to the control module 18 and is operated to energize the control module microprocessor. The AC operating voltage at terminals 34 is also applied to a silicon controlled rectifier-type, 24 volt power supply 46. The regulated output (24 V DC) from the power supply 46 is applied to a printwheel bank stepper motor 48 and a printwheel stepper motor 50 associated with the printing module 16. The regulated output is also coupled by an AC choke 52 to a capacitor 54. The internal capacitance within the 24 volt power supply 46 provides sufficient energy storage to continue to properly energize a switching regulator 56 should an AC power failure occur at terminals 34. In such event, the accounting module microprocessor 58 transfers information from the postage meter volatile memory (which may be internal or external to the microprocessor) via the data bus 66 to a nonvolatile memory 62. The switching regulator 56, in conjunction with a transformer with related circuitry, provide regulated output voltages used to energize the accounting module. A supply of plus five volts is developed by regulator 56 and is applied to the accounting module microprocessor 58, to NMOS nonvolatile memory 62, to the optic buffers (not shown) for the serial data bus 30 connected between the accounting and printing modules, to the printing module 16, and to the opto-interrupters 20-28. A supply of minus 30 volts is also developed across Zener diode 88 via transformer secondary 78 and is applied via an NPN transistor 100 and an NPN transistor 64 to the nonvolatile memory 62. The operation of transistor 64 is controlled by the accounting module microprocessor 58. The minus 30 volts is required in conjunction with a minus 12 volts (which is developed from a tapping 90 of the transformer and applied to the nonvolatile memory 62) and the plus five volts to enable the nonvolatile memory to have data written into the device. The switching regulator 56 functions to selectively apply the 24 volts developed across the capacitor 54 to the junction of a diode 66 and poled transformer primary winding 68. The frequency at which the regulator 56 operates or switches is determined by a capacitor 70 which controls the operating frequency of the supply. Primary winding 68 is further coupled to ground by a capacitor 72. Diode 66 and capacitor 72 form a complete circuit in parallel with the primary winding 68. The circuit path is through a point of fixed reference potential, here shown as ground. During quiescent operation, a voltage of +5 volts is developed across capacitor 72. This voltage is sensed and coupled via a series connected variable resistor 74 and a fixed resistor 76 to an input terminal on the switching regulator 56. This feed-back path controls the supply 56 to maintain a constant voltage across capacitor 72. For the component values shown, a voltage variation of appoximately 10 millivolts can occur across the capacitor 72. The step-up secondary winding 78 oppositely poled to the primary winding 68 is electromagnetically coupled via a mollypermoly core 80 to the primary winding 68. The secondary winding 78 is connected to ground at one end and has its opposite end coupled via a diode 82 which operates in conjunction with a capacitor 84 and current limiting resistor 86 to develop -30 volts across Zener diode 88 as already mentioned. A center-tap 90 on the secondary winding 78 is connected to a diode 92 which operates in conjunction with a capacitor 94 and a current limiting resistor 96 to develop -12 volts across a Zener diode 98. Because of the filtering provided by capacitor 72 and the inductance of the primary winding 68, the noise introduced by the switching transients in the primary circuit is minimized. In a like manner, the capacitors 84 and 94 and the inductance of the secondary winding 78, provide further filtering which also minimizes the noise introduced by the switching transients. The operation of the power supply system is described in greater detail in EP-A-0075824 (inventor Roland G. Miller) for Power Supply system filed concurrently herewith. A circuit is provided to ensure that the nonvolatile memory 62 is not energized by the -30 volts necessary for a writing operation after a particular voltage condition in the power down sequence has been reached. This ensures that even if data is put onto the nonvolatile memory bus 66 by the microprocessor 62, the data will not be written into the nonvolatile memory. This is particularly important because, although the micro-processor may be designed to turn off and not output data at a determined voltage level (for example, when the +5 volt supply drops below voltage +4.50 volts), it has been discovered that such microprocessors may become active again at even lower voltages such as +3 volts. Specifically, it has been discoverd with one particular type microprocessor designed to turn off at +4.5 volts that a range of around +3 to +2.2 volts exists where the device may become active again although within the supposedly inactive range for the device. For another type of microprocessor designed to turn off when the +5 operating voltage supply drops below +4.75 volts, it has been discovered that a range around +3.0 volts exists where the device may become active, again within the supposedly inactive range for the device. The -30 volt supply to the nonvolatile memory 62 is passed through the collector-emitter electrode current path of the NPN transistor 100. The collector electrode of the transistor is coupled via a resistor 102 to the +5 volts developed at capacitor 72. Base bias for the transistor 100 is obtained from a PNP transistor 104. The emitter electrode of the transistor 104 is connected by a 10 volt Zener diode 106 to the +24 volt DC supply 46. A resistor 109 provides a ground return for transistor 104. Resistors 108 and 110 are connected to the base electrode of transistor 100. A capacitor 112 is provided to further filter transients. In operation when the voltage at the AC lines fails, a power down routine is initiated. The routine may be initiated by a system such as that disclosed in the aforementioned US-A-4,285,050 for Electronic Postage Meter Operating Voltage Variation Sensing System. When the AC line voltage drops to a level such that the 10 volt Zener diode 106 no longer is operating in a break down mode, transistor 104 is biased out of conduction. As a result, transistor 100 is also biased out of conduction. This causes the +5 volts applied via resistor 102 to the collector electrode of transistor 100 to be applied to the emitter electrode of transistor 64. The +5 volts reverse biases transistor 64 and ensures that no information can be written into the nonvolatile memory 62 during the remainder of the power down cycle, as a supply of -30 volts is required to enable a WRITE operation in the nonvolative memory. For the various supplies and component values shown, by the time the output voltage of the +24 volt supply 46 decays to +7.5 volts, the +5 volts developed at capacitor 72 will begin to drop. By this time, however, the 10 volt Zener diode 106 has already been turned off for a voltage change of approximately 2 1/2 volts and the transistor 64 is, of course, already in a reverse bias condition. Thus, when the output voltage from the +24 volt supply drops to approximately +10 volts, transistor 64 is reverse biased and no data can be written by microprocessor 58 into nonvolatile memory 62. As the power continues to dissipate the transistor 64 remains reverse biased. Transistor 64 continues to be reverse biased through the decay cycle, until the voltage falls below the junction potential of the device, normally +.7 volts. By this time, however, the microprocessor has passed through the range of uncertain operating voltage and is completely inoperative. By this means, a further enhanced security is provided in the operation of the nonvolatile memory 62 and, additionally, a wider spectrum of microprocessor devices with concomitant cost advantages can be employed in the postage meter. Reference is now made to Figure 2. In this embodiment of the present invention a resistor 111 is added to the schematic circuit diagram shown in Figure 1 to apply the +5 volt supply directly to the WRITE voltage terminal. Thus, resistor 111 is connected between the collector electrode of transistor 64 and capacitor 72. This provides yet further enhanced memory protection over the circuit shown in Figure 1. In the embodiment of the invention shown in Figure 3, transistor 64, shown in Figures 1 and 2 is eliminated and the collector electrode of transistor 100 is directly connected to the WRITE voltage terminal. The structure eliminates the redundant protection afforded by both transistor 64 whose base bias is controlled by microprocessor 58 and transistor 100 whose base bias is dependent upon voltage levels in the postage meter's power supply systems. Protection is afforded in this case by control over the conductivity of the collector-emitter electrode current path of transistor 100. Reference is now made to Figure 4 which is a persective view of an electronic postage meter suited to incorporate apparatus according to the present invention. The postage meter 12 is detachably secured to a base unit 114 so as to form a letter slot 116 there-between at the front edge of the assembly. The base unit 114 may be mechanically of the type disclosed, for example, in US-A-2,934,009 issued to Bach et al for Sheet Feeding and Treating. The base incorporates a mechanical drive, not shown, for providing mechanical drive energy for the printing drum of meter 12. The postage meter 12 is an electronic postage meter in the sense that the accounting system within the meter, including the registers, is electronic as opposed to mechanical. Power is suppoied to the meter 12 via an AC power cord 118. The power cord 118 is connected to terminal 34 within the conductive shielding provided by the metal meter housing 120. A keyboard 122 and display 124 are provided and are connected to the control module 18 microprocessor and control circuit. Thus, improved protection is provided against unpredictable circuit operation when power failure occurs for any reason. The protection circuit ensures that information is not inadvertently written into a nonvolatile memory, which memory is particularly suitable for use as part of an electronic postage meter system. This form of proctection is particularly important in electronic postage meter systems with regard to ensuring the integrity of accounting data stored in the meter. The present invention ensures that erroneous information is not written into nonvolatile memory during a power down cycle. Thus, briefly summarized, there is a nonvolatile memory including a WRITE voltage (V GG ) terminal which when energized by a first predetermined polarity voltage enables the nonvolatile memory to have data written into memory locations. A computing means is operatively coupled to the nonvolatile memory for writing data into such memory location. First means are provided for generating a voltage of the first predetermined polarity, and second means are also provided for generating a second voltage differing from the voltage of the first predetermined polarity. Means are coupled to the first voltage generating means, the second voltage generating means and the WRITE voltage terminal of the nonvolatile memory for applying the voltage of the first polarity to the WRITE voltage terminal when a predetermined power condition exists and for utilizing the second voltage for causing a different voltage level from the first predetermined voltage to be applied to the WRITE voltage terminal when the predetermined power condition is not present. The control of the voltage levels applied to the WRITE voltage terminal is independent of the operation of the computing means. Thus, protection can be provided against improper data being written into the nonvolatile memory even if the computing means malfunctions during a power down operation.

Claims: An electronic postage meter system adapted to be energized by an external source (34) of operating voltage, comprising: printing means (16,48,50) for printing postage; accounting means including a microprocessor (58) coupled to said printing means (16,48,50) for accounting for postage printed by said printing means; nonvolatile MNOS memory (62) operatively coupled to said microprocessor (58) for storing accounting data even when said external source of operating voltage is not operating correctly, said nonvolatile MNOS memory (62) having a WRITE voltage supply terminal, coupled via a coupling device in the form of a switching device (64) or a direct connection to a WRITE voltage line (WCL) for providing said terminal with a first voltage of a first polarity to enable said nonvolatile MNOS memory to have data written into memory locations thereof by said microprocessor (58); said nonvolatile MNOS memory (62) including further a voltage supply terminal adapted to be energized by a second voltage of opposite polarity for energizing said nonvolatile MNOS memory to operate; first voltage generating means (78,82,84, 86,88) for providing said voltage of said first polarity; second voltage generating means (66,68,72) for providing said voltage of said opposite polarity; coupling means (102) connected between said voltage supply terminal and said second voltage generating means (78,82,84,86,88); sensing means (104,106,109) arranged to sense when said external source of operating voltage is above or below a predetermined level; and switching means (100) coupled to said first voltage generating means and responsive to said sensing means for applying said voltage of said first polarity to said WRITE voltage line when said external source of operating voltage is above said predetermined level and for removing said voltage of said first polarity from said WRITE voltage line when said external source of operating voltage falls below said predetermined level, characterized in that: said switching means (100) is operable to remove said voltage of said first polarity from said WRITE voltage line as aforesaid independently of the operation of said microprocessor; said switching means (100) is coupled to said second voltage generating means (66,68,72); and said switching means (100) is operable independently of the operation of said microprocessor to apply said voltage of said opposite polarity to said WRITE voltage line when said external source of operating voltage falls below said predetermined level in order to prevent a writing operation being performed in said nonvolatile MNOS memory. A system according to claim 1 characterized in that said switching device is an input transistor (64) whose control electrode is coupled to said microprocessor. A system according to claim 2 characterized by a resistor (111) connected between the WRITE voltage supply terminal and said second voltage generating means. A system according to any one of claims 1 to 3 characterized in that said switching means (100) is a transistor whose controllable path is coupled between said first voltage generation means and said WRITE voltage line. A system according to claim 4 characterized by means (108,110) for coupling the control terminal of said transistor (100) to said sensing means (104,106,109) such that the sensing means controls the conductivity of the controllable path of said transistor (100). A system according to claim 5 characterized by said sensing means including a coupling transistor (104) coupled between said first voltage generating means and a source (46) of DC operating power energizable by said external source (34) of operating voltage, said coupling transistor (104) being arranged to control the bias applied to said control electrode of said switching means transistor (100). A system according to claim 6 characterized in that the controllable path of said coupling transistor (104) is connected in series with a Zener diode (106), this series connection being connected between said first voltage generating means (92,94,96,98) and said DC power source (46). A system according to any one of the preceding claims including a data bus (66) coupled between said nonvolatile memory (62) and said accounting means (58). A system according to any one of the preceding claims characterized in that said coupling means is an impedance (102). A system according to claim 9 wherein said impedance is a resistor (102).

Inventors: ECKERT, ALTON BROOKS
Applicants: PITNEY BOWES INC.
Application year: 1982
Main classification: G07B17
IPC codes: G07B17, G11C16, G11C7, G06F12