EP1154382A2 - Method for manipulation-proof control of print data and internal interface circuit for franking machines - Google Patents

Abstract

Prior to data transfer for an individual printing format, an encoded data exchange takes place between a printing head electronic unit (30) and a printing data control unit (700). Code generators (32,703) create a new encoded unique code in both units for clearing the printing head and quitting. After finishing data transfer for an individual printing format, the printing head is automatically locked.

Description

The invention relates to a method for manipulation-proof print data control and a Interface circuit internal to the franking machine according to that in the preamble of claims 1 and 5 specified type.

Franking machines have at least one transport device, Input, storage and display means and a pressure control unit for a printing device on what print patterns toward you this printing device moved to be printed Record carrier prints. Such printing devices, especially for an electrothermal Printing using an ink ribbon or transport devices are equipped with actuators and sensors, which controlled via a circuit arrangement or are queried (US 4,746,234).

Sensors used to transport the record carrier detect, solve, for example Printing process. Other sensors detect that Position of the counter pressure roller or monitor the ongoing printing.

A shaft of the transport device or coil one moved relative to the record carrier Color carrier that transfers the color particles coupled to an encoder, which clock signals for printing control during the printing process provides. All sensors or actuators are directly or indirectly through a special Circuit arrangement with the control unit, in particular a microprocessor control unit, connected.

For a thermal transfer printing process is already from DE 38 33 746 A1 via a control unit actuated switching unit for one Known printhead that contains resistance elements. A selective control with preheating the Resistance elements serves to reduce the Heating power when printing. To control one Printhead becomes energy for each pixel of the printed image provided and a Print pattern on a relative to the ribbon printed on the recording medium to be printed, by removing the ribbon from the paint layer when the associated heating resistor is heated in the print head on the record carrier transmits.

Inkjet printers are also used to frank mail suitable. According to the used Printing principle must the circuit arrangement to the required actuators and sensors adapted become.

An ASIC is known from EP 465 236 A2, which a circuit for pressure control, for engine control and includes for billing. The circuit for pressure control includes a memory for fixed and another for variable data, which with overlay the fixed data. An engine controller is for actuating a motor drive provided depending on the mailpiece feed. A sensor delivering speed signals is standing via the motor controller with the pressure control in Connection. The high is undoubtedly an advantage Tampering security alone results from the limited number of starting points for a manipulation due to the use of a single ASIC. One disadvantage of using one The only ASIC is the lack of usability for different franking machines, which one different pressure control module accordingly a realized franking machine system or Show Poststrasse.

But should different types of franking machines then a variety of must be produced Circuits (ASIC's or / and other components) be provided. Especially the large number of components and circuits then offer starting points for manipulation, if no alternative Effort driven and a security case is used. Differentiate between franking machine types accordingly in shape and equipment of the mail volume to be processed and thus also regarding a different number Sensors and actuators.

This is periodic polling from EP 231 452 A2 of sensors according to a software routine a central processing unit (CPU), preferably a microprocessor known.

The disadvantage of this solution is a high one Computing time due to periodic sampling of the sensors. This disadvantage is exacerbated if it is a particularly time-critical Query. To get to one as quickly as possible To be able to react to a change in state Polling frequency can be selected high. Consequently the microprocessor spends a large proportion its computing time with the query.

In US 5,267,172 there is already a serial Interface proposed in a franking machine been between a microprocessor and an ASIC is arranged and on which Transfer address, command and data serially to the ASIC become. The disadvantage is that time-critical Queries cannot be realized and none automatic work of the interface is what Computing time in the microprocessor binds.

The latter disadvantage also applies a data processing system known from US 5,199,105 to. For a universal asynchronous receiver / transmitter module is there first shift register for outputting the data and a second shift register for reading the data as well as a programmable comparison register proposed, to trigger interrupt when a specific data byte over the serial channel Will be received.

The task is to create a procedure and an internal franking machine To develop interface circuitry which have the disadvantages of the prior art Technology avoids and for a variety of franking machine variants realizable at low cost is without manipulation security Reduce.

A subtask is to develop one Print data control through less computing time the CPU is bound and the function or. Manipulation security is maintained.

The object is achieved with the features of claims 1 and 5 solved.

The invention is based on the consideration that Adaptability of the electronic control different franking machine types by one Interface circuit internal to the franking machine improve.

Within a security housing, a microprocessor of a first circuit part, in which only security-relevant data are processed, is connected to a second circuit part according to the invention, in which the remaining data are traded for the respective type of franking machine. This second circuit part forms an internal franking machine interface to the first circuit part.
The internal interface franking machine is advantageously designed as a system-specific ASIC.

It is assumed that to control a electronic printhead and the actuators or Sensor query the microprocessor of the first Circuit part on the second circuit part accesses. The microprocessor non-periodically queried or at data transmitted.

The circuit part for safety-relevant data is the same for all franking machine types educated. The second circuit part (ASIC) for the rest of the data is according to the type of franking machine as an internal interface to the first Circuit part formed.

The second circuit part (ASIC) is the internal franking machine Interface circuit. The latter has a print data controller. For Creation of print data control according to the The sub-task is the internal franking machine Interface circuit with send and receive registers for the storage of data transmitted in parallel Data and with a shift register for that Series / parallel or parallel / series conversion of the from or to the print head via a print register transmitted data, equipped.

Due to a small number of lines for Base manages to be an affordable solution for to create a meter / base separation.

According to the invention, the print data control becomes Security module expanded and offers in addition to the targeted Relief of the control unit CPU as well a higher security against manipulation against fraudulent Using the printhead in conjunction with special printhead electronics. According to the invention is one in each code generator Unity, i.e. in printhead electronics and Security module, independently of each other a code generated and transferred to the other unit. Comparators check the received activation or Acknowledgment code with the expected code. If correct becomes the printhead for a single print image unlocked. The image to be printed is then in "Plain text" (unencrypted) transmitted. To The print head is the end of the data transfer automatically locked again and must be with the help of a further coded data exchange unlocked become. A new code is encoded for each print image Data record for activation or acknowledgment creates a record of the activation process cannot be reused.

Another variant is according to the invention provided that the print data control a has third state machine, the input side with a mode register group for setting the operating mode and on the output side with Control inputs of the transmit shift register, one Test circuit and a pressure register connected is to one of a first connectable code generator submitted second receipt code under Controlled by the third state machine in insert a test shift register, where in Test shift register the second receipt code available in parallel and the test circuit according to a set security printer mode is trained, the serial Data transfer between print register printhead electronics on the one hand and the send shift register on the other hand, to monitor the bits received to monitor for predetermined changes in state, around an interrupt to the control unit if necessary and around thus a DMA-controlled print data transfer to Trigger printhead.

Figur 1,

Blockschaltbild der Schaltungsanordnung für Meter und Base,

Figur 2,

Blockschaltbild der frankiermaschineninternen Schnittstellenschaltung,

Figur 3,

Blockschaltbild für eine erste Variante der erfindungsgemäßen Druckdatensteuerung mit Testschaltung,

Figur 4,

Blockschaltbild für eine zweite Variante der erfindungsgemäßen Druckdatensteuerung mit Sicherheitsmodul.

Advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. Show it:

Figure 1,

Block diagram of the circuit arrangement for meter and base,

Figure 2,

Block diagram of the franking machine internal interface circuit,

Figure 3,

Block diagram for a first variant of the print data control according to the invention with test circuit,

Figure 4,

Block diagram for a second variant of the print data control according to the invention with a safety module.

1 shows a block diagram of a Circuit arrangement for a franking machine. The Circuit arrangement can be divided into two parts, namely Assign meter and base, the base at least the motors and other actuators, sensors and the Printhead with associated control electronics contains. The meter contains the first circuit part the actual control that comes with a Input / output module 4 and in particular with one second circuit part, the invention Interface circuit internal to the franking machine connected, which is advantageously as ASIC 14 can be trained. The control includes in known way a clock / date block 8, one Character store 9, a cost center store 10, a non-volatile memory 5, program memory 11 and memory 7, which with a Microprocessor in communicative connection.

In the clock / date block 8 time data and that Date even when the franking machine is switched off generated. The input / output module 4 provides, for example via an RS 232 interface Connection to the modem 23 and possibly to the scale 22. The latter can be part of the base. Moreover are the display controller 3 and the module 4 Keyboard 2 connected.

The input data is stored in the non-volatile memory (NVM) 5 saved so that the last setting received before the franking machine was switched off remains. The operating program is in the program memory 11 and fixed dates, for example for a Advertising slogan, saved. In the cost center memory 10 the current accounting data Depending on the cost center, non-volatile before each print saved.

The corresponding is in the character memory 9 Character set available. According to the inputs corresponding characters as pixel data in the Pixel memory 7 saved.

The microprocessor is used as a control unit 6 for the entire franking machine and is connected to blocks 4, 5, 7 to 11 of the first circuit part 1 via address lines A and data lines D and via address, data and control lines (A, D, S) connected to the second circuit part 14, which is designed as an ASIC. The above-mentioned blocks are addressed by the microprocessor in accordance with the memory control signals S _s generated in the decoder of the ASIC.

The function-determining ones - in FIG. 1 shown - blocks of the first circuit part partial or total to at least one physical Component are summarized and others Measures should be taken to prevent tampering difficult by unauthorized persons. The Function of these blocks and such measures are for example in the German patent application DE 43 44 476 A1 explained in more detail.

The invention is illustrated in the following embodiment together with Figures 2 to 4 explained in more detail.

The circuit part 14, shown in more detail in FIG. 2, for the interface inside the postage meter machine, which is designed in accordance with the type of postage meter machine, has a decoder 300 for providing the memory control signals, an actuator / sensor controller 400, an interrupt controller 600 and a print data controller 700. The address lines A0 to A3 and data lines D and control lines S are connected to all blocks 300, 400, 600 and 700. Address lines A13 to A19 are also present on the decoder. Decoder 300 provides memory control signals S _s for blocks 400, 600 and 700. The block 400 for the actuator / sensor control outputs a signal I _i on the output side to the block 600 for the interrupt control. The block 600 is connected on the output side to the control unit 6 via the lines for the data and control signals I _o (FIG. 1). The ASIC circuit part 14 is equipped with an input s for connection to the sensors of the base and with an output a for connection to the actuators of the base of the franking machine via a register unit 28 (FIG. 1). More detailed information on the actuators / sensors and on the interrupt control can be found in EP 716 398 A2.

The register groups of all blocks 300, 400, 600 and 700 can - in a manner not shown - within of the ASIC 14 form its own block 500, which in communication with the other blocks stands.

A sensor for time-critical data is the encoder 13. On the one hand, this is - in the manner shown in FIG. 1 - directly at the input e of the control unit 6 and on the other hand is connected to the input e of the second circuit part (ASIC) 14. The encoder acts on a DMA controller present in the control unit 6.
The DMA controller reads out a complete stamp image from the pixel memory (RAM) 7 and reads it into the print register (DR) of the print head 16 in print column-wise fashion via the ASIC print data controller 700. The encoder 13 acts directly on the print data controller 700 by supplying an external trigger signal for the transfer of the print data for the individual print columns to a second state machine 701.

The print data controller 700 is in FIG a first variant explained. A third State machine 701 is with a transmit shift register 710 and with a test shift register 720 connected to the control of data transfer by means of a signal CLOCKOUT. The Send shift register 710 sends that from the DMA controller delivered bytes to the print register (DR) 15. A series-parallel conversion takes place here the data for the printhead electronics of the printhead 16. The printhead 16 contains for temporary storage the parallel print data register, which with a signal LATCH corresponding to the Encoder signal at input e can be controlled, as well Driver, which is signaled by a STROBE signal from the Control unit 6 can be controlled. The drivers control the actual printing elements of the Printhead 16.

The ASIC 14 can be used in conjunction with the first Circuit part 1 based on a test circuit 702 serial data transfer can be monitored. The Test shift register 720 can get data from the print register 15 received serially, which after serial-parallel conversion from the control device 6 can be read via the data line D if necessary can.

In addition, the ASIC 14 can be used in conjunction with the first circuit part 1 due to a local Loop and by means of the test circuit 702 serial data transfer can be tested. Is to provided that the bits of the Send shift register 710 for serial print data Purpose testing via a local loop LOCAL LOOP and into a test shift register by means of a test circuit 702 720 can be read.

Through special mode registers shown in Figure 3 750 can from the control unit 6 via the data line D set the operating mode become. The number of bytes, the type the transfer (with or without a byte counter) and the Clock rate of the shift clock can be predetermined.

Additional registers can be in register block 500 of the ASIC's 14 can be provided and can be connected with the third state machine 701 more Data, clock or control signals to the printer register 15 and deliver the printhead electronics, see above that the control even when using different Printheads becomes possible.

The problem of tamper security one external to the meter in the base Printhead was created using special printhead electronics and with special circuit measures solved in the print data control unit 700, which the control unit 6 of pressure monitoring tasks relieve. This will be an activation realized for a single print image. Unlock signals or monitoring data can also be transmitted separately, but this is more complex would be like a serial transmission.

FIG. 4 is a block diagram for a second variant of the print data control according to the invention with training as a security module shown. The on an expanded printhead hardware connected print data control unit 700 - According to the embodiment shown in Figure 3 expanded to include a second code generator 703, a multiplexer 709, a demultiplexer 725 and a second comparator 723. In addition, the-in 3 - printhead hardware by one Printhead electronics 30 expanded, which one first code generator 32, a demultiplexer 35, a first comparator 33, a monitoring module 36 for print data length monitoring for a single activated print image, first and second switch means 34, 37 and a fourth State machine 31 includes.

The modification of the extended printhead hardware compared to the print data control unit shown in FIG on the one hand results from a very large number of print data to be transmitted, for example 200 dpi (dot per inch) for one Pressure column. Also the one shown in Figure 3 Send shift register 710 or the print register DR 15 need to transfer data for a print column be designed. The printing is done column by column preferably on an envelope if the print column data parallel to the printhead STROBE signal is switched to the printhead.

On the other hand, with the special printhead electronics a need for security against manipulation met. Before printing begins the trained according to the invention to the security module Print data control in the meter for special Printhead electronics in the base an activation code transmitted. Under the control of the fourth State machine 31 is the one after Series / parallel conversion in the pressure register 15 cached activation code via a Demultiplexer 35 to a first comparator 33 created. From the first code generator 32 under the control of the fourth state machine 31 generates a predetermined code and the first Comparator 33 supplied, which is a comparison performs. If the comparison is positive, a Activation signal to a monitoring module 36 Print data length monitoring for a single unlocked print image. Otherwise the print head remains locked. At the same time with the aforementioned activation, the predetermined Code via first switch means 34 den Pressure register 15 supplied, which the predetermined Code as activation code serial to the print data control unit 700 transmitted. As the first switch 34 are preferably field effect transistors or other comparable taxable electronic switches.

According to the invention, such a version has a Print data controller 700 a third state machine 701 on the input side with a Mode register group 750 for setting the Operating mode and output side with control inputs the transmit shift register 710, a test circuit 702 and the external print register 15 is to be switched on from a first Code generator 32 issued receipt code under Controlled by the third state machine 701 into a test shift register 720. in the Test shift register 720 is the acknowledgment code can be called up in parallel and the test circuit 702 is according to a set security printer mode trained the serial data transfer between print register 15, print head electronics 30 on the one hand and the transmit shift register 710 on the other hand, to monitor the bits received to monitor for predetermined changes in state. By the second comparator 723 and the interrupt control 600 becomes a monitoring circuit educated. An input of a - in Figure 4 not shown - priority encoder is about a-not shown - D flip-flop with that of the second Comparator 723 output signal J charged which is a match signals. If there is agreement, the Interrupt control 600 generates an interrupt.

Thus, if necessary, an interrupt for Control unit 6 are transmitted to subsequently a print data transfer to the print head trigger. When transferring over the DMA channel is started, it runs automatically without Participation of the control unit 6 (CPU). Thereby the control unit 6 (CPU) is relieved.

The interface circuit inside the franking machine is equipped with send and receive registers for the storage of data transmitted in parallel Data and with a shift register for that Series / parallel or parallel / series conversion of the from or to the print head via a print register transferred data.

a) Durchführung eines codierten Datenaustausches, wobei in der Druckkopfelektronik 30 und in der Druckdatensteuereinheit 700 unabhängig voneinander ein einzigartiger Code erzeugt und jeweils zur anderen Einheit 30, 700 übertragen wird,

b) Überprüfen der empfangenen Freischalt- bzw. Quittungscode mit dem erwarteten Code mittels Vergleicher, wobei bei Korrektheit der Druckkopf für ein einzelnes Druckbild freigeschaltet und das zu druckende Bild dann übertragen wird,

c ) Überwachen des von der Druckkopfelektronik 30 übermittelte Codes in der Druckdatensteuereinheit 700 und Bildung eines Interruptsignals bei Korrektheit, wobei das Interruptsignal zur Steuereinheit 6 übertragen wird, um damit anschließend eine DMA-gesteuerte Druckdatenübertragung zum Druckkopf auszulösen,

d) automatisches Sperren des Druckkopfes nach Beendigung der Datenübertragung für vorgenanntes einzelnes Druckbild und

e) Erzeugung eines neuen codierten einzigartigen Codes zur Freischaltung bzw. Quittierung, um den Druckkopf wieder für ein folgendes Druckbild freizuschalten.

The procedure for manipulation-proof print data control is characterized by the following steps:

a) carrying out a coded data exchange, a unique code being generated independently of one another in the printhead electronics 30 and in the print data control unit 700 and each being transmitted to the other unit 30, 700,

b) checking the received activation or acknowledgment code with the expected code by means of a comparator, the print head being activated for a single print image and the image to be printed being transferred if correct,

c) monitoring the code transmitted by the printhead electronics 30 in the print data control unit 700 and generating an interrupt signal if correct, the interrupt signal being transmitted to the control unit 6 in order to subsequently trigger a DMA-controlled print data transfer to the printhead,

d) automatic locking of the print head after completion of data transmission for the aforementioned individual print image and

e) Generation of a new coded unique code for activation or acknowledgment in order to activate the print head again for a subsequent print image.

After checking the Unlock codes received for exactly one impression unlocked. Print data length information becomes the print head as part of a coded data exchange, the u.a. the length of the print Image in bytes or in a predetermined number contains to pressure columns, transmitted. Preferably becomes the aforementioned print data length information from the demultiplexer DEMUX 35 into the monitoring module 36 transmitted for print data length monitoring, before that sent to the printhead Print data transmission signal the unencrypted Contains image data. In the state of activation is a print data length monitoring for the unencrypted image data performed to the Termination of data transmission for the aforementioned to determine the individual print image. Locking the Printhead will be reached when the predetermined print data length information Print data length triggered.

A method for manipulation-proof print data control, after another version works with several generated codes at the same time. It is provided that to carry out the encoded Data exchange code independently of each other are generated to compare the Printhead electronics transmitted codes with a generated first code and a comparison of the codes transmitted to the print data control unit a second code.

According to the invention, the aforementioned has another version for such a print data controller 700 with training a second code generator for the security module 703 for generating one for everyone Imprint unique unlock codes and one third state machine 701 on the input side with a mode register group 750 for Setting the operating mode and on the output side with Control inputs of the transmit shift register 710, a test circuit 702 and the external print register 15 is connected to one of one emitted first connectable code generator 32 second receipt code under the control of the third state machine 701 into a test shift register 720 to insert. In the test shift register 720, the second acknowledgment code is available in parallel before and the test circuit 702 is corresponding a set security printer mode, serial data transfer between print registers 15, printhead electronics 30 on the one hand and the transmit shift register 710, on the other hand, around the received bits to predetermined ones Monitor changes in state. Thus, if necessary an interrupt is transmitted to the control unit 6 in order to subsequently transfer a print data trigger to the printhead. If the Transmission over the DMA channel is started, this runs automatically without the involvement of the control unit 6 (CPU) onwards. This also makes the Control unit 6 (CPU) relieved.

In the print data control unit 700, which the Control unit 6 of pressure monitoring tasks relieve, it is provided that at the parallel Output of test shift register 720 a first Input and at the parallel output of a second Code generator 703 a second input of a digital comparator 723 for checking the second receipt codes is connected, the parallel data bits of the second acknowledgment code with those from the second code generator 703 supplied data bits of a first activation code be compared and if there is a mismatch Error message for the monitoring circuit (723, 600) is transmitted. The entrances are preferably of the digital comparator (723) with internal Buffer storage for temporary storage before a Check the code provided. Internally comes again an XOR link is used.

The control unit CPU 6 is over a DMA channel connected to transmit shift register 710. At Compliance of the aforementioned code, which on second comparator 723, the Transmission of the error message for interrupt control 600 interrupted and instead Agreement signals. To report the match becomes a signal J for interrupt control (600) transmitted. From interrupt control 600 then an interrupt is generated and delivered to the control unit CPU 6, whereby is caused by the control unit CPU 6 Print data to the transmit shift register via the DMA channel 710 are transmitted.

Between the transmit shift register 710 and the second code generator 703 or the control unit CPU 6 is a multiplexer MUX 709 connected to the second activation code or via the DMA channel transmitted print data in the send shift register Invite 710.

With the help of special printhead electronics and With special circuit measures an activation will be realized for a single print image, by between the pressure register DR 15 and the Print head 16 arranged the print head electronics 30 is and after that activation the print data transfer to the print register DR 15 via the print head electronics 30 to printhead 16 under surveillance done by the printhead electronics 30.

The printhead electronics 30 has a fourth State machine 31 on the input side with a clock signal CLOCKOUT from the third state machine 701 and from a monitoring module 36 is supplied with an output signal and on the output side with a control input of a first one electronic switch 34, with a control input a second electronic switch 37, with a first code generator 32 and with a Control input of a demultiplexer DEMUX 35 connected is, at a first output of the Demultiplexers DEMUX 35 for parallel data transfer an internal buffer for the printhead DK 16 is connected.

It is also contemplated that at the parallel Output of the first code generator 32 a first Input and at the second output of the demultiplexer DEMUX 35 a second input of a digital Comparator 33 for checking the activation code is connected, the parallel retrievable data bits of the second activation code with those supplied by the first code generator 32 Data bits of a first acknowledgment code compared an error message if they do not match is transmitted to the monitoring module 36, that the monitoring module 36 otherwise at Agreement is unlocked and that from fourth state machine 31 of the demultiplexer DEMUX 35 for parallel data transmission via its first output to an internal buffer of the monitoring module 36 switched becomes.

The monitoring module DLC 36 preferably has Counters to act on columns or bytes to carry out a pressure length monitoring. The counter DLC 36 generates an output signal to the fourth state machine 31 upon reaching one predetermined print length.

The fourth state machine 31 acts on the Control input of the second electronic switch 37 to when a predetermined printing length is reached a signal supplied by encoder 13 LATCH from internal buffer of the print head DK 16 switch off, so that no further print data can be printed by the print head DK.

It is also envisaged that the fourth State machine 31 the control input of the first electronic switch 34 applied and from first code generator 32 into the print register second receipt code is read, which for Print data control 700 is transmitted. Advantageous are the inputs of the digital comparator 33 with internal buffer storage for temporary storage before checking the code.

Because this franking machine internal interface circuit to the base a number of serial Interfaces with any expansion options forms, this enables an adaptation to the various franking systems and to each base Franking machine, on the one hand for the purpose of sensor query and for actuator setting, with a non-periodic Query by a microprocessor 6 and with an interrupt controller 600 and on the other hand for a print data controller 700 with operating mode setting and testing options.

The different systems require differently designed decoders 300 and thus different ASICs. Relative system independence can, however, be achieved using an additional decoder 900, shown in dashed lines in FIG. 1, ie if the internal decoder 300 is used only partially or not in order to control the blocks of the first circuit part for security-relevant data by means of memory control signals S _s .

The invention is not based on the present embodiment limited. Rather is a number of variants conceivable, which of the shown Solution also with different types Make use.

Claims (15)

Method for manipulation-proof print data control, by means of at least partially encrypted information that is exchanged between two units, characterized by the steps: a) performing a coded data exchange, a unique code being generated independently of one another in a printhead electronics (30) and in a print data control unit (700) and each being transmitted to the other unit (30, 700), b) checking the received activation or acknowledgment code with the expected code by means of a comparator, the print head being activated for a single print image and the print image to be printed then being transferred if it is correct, c) monitoring the code transmitted by the printhead electronics (30) in the print data control unit (700) and formation of an interrupt signal if correct, the interrupt signal being transmitted to the control unit (6) in order to subsequently trigger a DMA-controlled print data transfer to the printhead, d) automatic locking of the print head after completion of data transmission for the aforementioned individual print image and e) Generation of a new coded unique code for activation or acknowledgment in order to activate the print head again for a subsequent print image. Method according to Claim 1, characterized in that, for carrying out the coded data exchange, codes are generated independently of one another in order to carry out a comparison of the code transmitted to the print head electronics with a generated first code and to compare the code transmitted to the print data control unit with a second code. Method according to Claim 1, characterized in that, in the state of activation, a print data length monitoring is carried out for the unencrypted image data in order to determine the end of the data transmission for the aforementioned individual print image and that the blocking of the print head is triggered as soon as a print data length specified by print data length information is reached . Method according to Claim 1, characterized in that the print data length information is transmitted to the print head as part of a coded data exchange, the code including the length of the image to be printed in bytes or as a predetermined number of print columns and in a monitoring module (36) for monitoring the print data length is transmitted before the print data transmission signal transmitted to the print head contains the unencrypted image data. Interface circuit internal to the postage meter machine equipped with send and receive registers for the storage of data transmitted in parallel and with a shift register for the serial / parallel or parallel / serial conversion of the data transmitted from or to the print head via a print register,
characterized in that a print data controller (700) is equipped with a transmit shift register (710), a test circuit (702) and a monitoring circuit (723, 600) and in that a printhead hardware is equipped with a print register (15), the print register (15 ) and the transmit shift register (710) are connected to the test circuit (702) in order to monitor the received bits for a predetermined change in state and that the test circuit (702) is connected to a control unit (6) which is connected via the transmit shift register ( 710) provides at least print data for transmission to the print head, the test circuit (702) being designed in accordance with a set security printer mode to monitor the serial data transfer between the send shift register (710) of the print data controller (700) and the print register (15), and wherein the Monitoring circuit (723, 600) is designed to transmit an interrupt to the control unit (6) in order to carry out the transfer trigger the print data to the print head. Interface circuit internal to the postage meter machine according to claim 5, characterized in that the print head hardware has a first code generator (32) which can be connected to the print register (15), that a print data controller (700) has a third state machine (701) which on the input side has a mode register group (750) Setting the operating mode and on the output side is connected to control inputs of the transmit shift register (710), the test circuit (702) and the print register (15) in order to receive an acknowledgment code issued by the first connectable code generator (32) under the control of the third state machine (701) to be inserted into a test shift register (720) of the test circuit (702), the acknowledgment code which is emitted being present in the test shift register (720) in parallel by a digital comparator (723). Interface circuit internal to the postage meter machine according to claim 6, characterized in that the third state machine (701) is acted upon on the input side with an encoder signal (e) and with DMA control signals and with a signal from a mode register (750), and in that the third state machine (701) applies the shift register (710) and optionally a test circuit (702) controls and cooperates with the control unit (6) so that the operating mode of the print data control (700) is set, with the test circuit (702) and the control unit (6) checking means for checking the operation according to the set operating mode. Interface circuit internal to the postage meter machine according to claim 7, characterized in that an operating mode is set for the test circuit (702) via special mode registers (750) and via the third state machine (701) in order to test the bits of the transmission shift register (710) for serial print data via a read local loop into a test shift register (720), whereby a series / parallel conversion takes place and that the control unit (6) is programmed, the testing in connection with means (4, 5, 7 to 11) of a first circuit part (1) in to take the printing breaks. Interface circuit internal to the postage meter machine according to claim 7, characterized in that the number of bytes, the type of transfer and / or the clock rate of the shift clock can be preset via mode registers (750). Interface circuit internal to the postage meter machine according to claim 6, characterized in that the print data controller (700) has a second code generator (703), that a first input at the parallel output of the test shift register (720) and a second input at the parallel output of a second code generator (703) of the digital comparator (723) for checking the acknowledgment code is connected, the data bits of the acknowledgment code which can be called up in parallel being compared with the data bits of an activation code supplied by the second code generator (703) and a signal (J) for reporting if they match Interrupt control (600) is transmitted. Interface circuit internal to the postage meter machine according to claims 5 and 10, characterized in that the control unit CPU (6) is connected to the transmit shift register (710) via a DMA channel, one of which is output by the interrupt controller (600) to the control unit CPU (6) Interrupt is caused that the control unit CPU (6) via the DMA channel print data to the transmit shift register (710) is transmitted. Interface circuit internal to the postage meter machine according to claim 5, characterized in that a print head electronics (30) is arranged between the print register DR (15) and the print head (16) and after the activation the print data transfer to the print register DR (15) via the print head electronics (30) to the print head ( 16) under the supervision of the printhead electronics (30). Postage meter internal interface circuit according to claim 12, characterized in that that the printhead electronics (30) has a fourth state machine (31) which is acted upon on the input side by a clock signal CLOCKOUT from the third state machine (701) and by a monitoring module (36) with an output signal and on the output side with a control input of a first electronic switch (34) , with a control input of a second electronic switch (37), with a first code generator (32) and with a control input of a demultiplexer DEMUX (35), wherein at a first output of the demultiplexer DEMUX (35) an internal buffer of the Printhead DK (16) is connected, that at the parallel output of the first code generator (32) a first input and at the second output of the demultiplexer DEMUX (35) a second input of a digital comparator (33) for checking the activation code is connected, the data bits of the activation code which can be called up in parallel with the data bits of an acknowledgment code supplied by the first code generator (32) are compared and if there is a mismatch, an error message is sent to the monitoring module (36) that the monitoring module (36) will otherwise be activated if there is a match and that the fourth state machine (31) of the demultiplexer DEMUX (35) for parallel data transmission via its first output to an internal buffer of the monitoring module (36), and that the monitoring module (36) has a counter DLC to carry out pressure length monitoring in columns or bytes. Interface circuit internal to the franking machine according to claim 13, characterized in that that the counter DLC generates an output signal to the fourth state machine (31) when a predetermined pressure length is reached, that the fourth state machine (31) acts on the control input of the second electronic switch (37) in order to switch the encoder (13) when a predetermined pressure length is reached switch off the supplied signal LATCH from the internal buffer of the print head DK (16), so that no further print data can be printed by the print head DK (16). that the fourth state machine (31) acts on the control input of the first electronic switch (34) and a second acknowledgment code is read into the print register by the first code generator (32) and is transmitted to the print data controller (700). Interface circuit internal to the postage meter machine according to one of the preceding claims 5 to 14, characterized in that a multiplexer MUX (709) is connected between the transmission shift register (710) and the second code generator (703) or the control unit CPU (6) in order to use the activation code or to load the print data transmitted via the DMA channel into the transmission shift register (710) and that the inputs of a digital comparator (723, 33) are provided with internal buffer memories for temporary storage before the code is checked.

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