ST AN840 APPLICATION NOTE
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1. Ti AN840 yf APPLICATION NOTE Coded lock using the ST6 REALIZER INTRODUCTION The trend is to provide more and more applications with security features This is requested to insure data confidentiality access control or simply user identification Non Volatile Memory is usually required to store the identification or secret code With the embedded EEPROM provided on the ST62 MCU one chip solutions can be achieved with the associated cost and density advantages A coded lock system has been developed with the ST6 REALIZER environment and is described in this note This development tool is used to get an automatic generation of the application software June 2008 Rev 2 1 7 Coded lock using the ST6 REALIZER 1 APPLICATION OVERVIEW The application described here consists of a coded lock for a door A secret code is loaded into the lock system to allow the door to be unlocked only if the same access code is entered When loaded the secret code is stored in the non volatile memory EEPROM embedded in the ST62 MCU This ensures that the data is retained even after a voltage cut off and insures the security is maintained along the time The application provides the following features Secret code recording 3 digits Recognition of entered access code Door lock control All the featured functions of the system are managed in the final application under software control by the MCU However using the ST6 REALIZER2. allows this application software to be generated by a functional description of the system Thus the software development can be achieved by a system oriented or hard ware like description Only the core of the application the secret code storage in EEPROM and the code recognition are de scribed as a generic base for various applications Any kind of user interface could be used keyboard IR or RF solution for instance while the output signal can activate any kind of circuit In the present case it is assumed that the user interface provides the following 4 inputs Digit reception flag Digit value 0 9 Change secret code Lock the door The digits used for the code are serially received announced by the activation of a flag 2 PRACTICAL REALISATION 2 1 Functional description By restricting the application description to its core the operations sequencing the secret code storage in the EEPROM and the code recognition the resulting application block diagram is represented in Figure 1 Figure 1 Block diagram of the coded door lock Lock the door S ace Change secret code Sequencing Dh estes Digit Reception Flag Control D 12 5 S Digit value ere gt Code o to door locking Recognition system VR02063 2 7 Coded lock using the ST6 REALIZER 2 1 1 Sequencing control The most important feature is the sequencing control of all the operations Two main
3. items must be con sidered the transition between the different working modes Door locked Access code entry Door un locked and Secret code entry and the management of the serial flow of the numeric values received through the user interface The transition between the working modes follows conditional rules described in the ST6 REALIZER with the help of a state machine as described in Figure 2 where four states are existing Door locked Code recognition Door unlocked Secret code entry Figure 2 State machine description for sequencing control Wrong Code Door locked amp recognition f One digit received Right Code Last digit Change Code The conditional occurrences are generated either through the user interface Lock Change secret code or through some functional sub blocks of the application One digit received Right code Wrong code Last digit For instance the occurrence of the condition One digit received in the Door locked state initi ates the process Code recognition The management of the serial flow of the digits entered 0 9 is achieved with a counter of received digits Figure 3 Depending whether it is the 1st the 2nd or the 3rd digit In the case of a 3 digit code the nu meric value issued by the interface is stored in the associated memory location When the 3rd digit is re ceived the counter is reset In addition the reception flags of the 1st digit and
4. 3rd digit are used in the state machine to initiate respectively the code recognition and conclude the Secret code entry 3 7 Coded lock using the ST6 REALIZER Figure 3 Management of the digits reception 1st_Digit X One digit received Digit Reception Flag 2nd_Digit Sra Digit X Last digit init 0 type bit Z Z4 2 1 2 Secret code storage in the EEPROM Thanks to the ST6 REALIZER the EEPROM Non Volatile Memory can be managed as a standard bista ble component R S Latch D Latch Shift Register or Counter In the present case each EEPROM location is symbolised by a specific D Latch component providing the Non Volatility feature This component provided within the ST6 REALIZER library has the advantage of being multitype This means the same symbol can be used whatever the input type Bit Byte Word Inte ger or Signed variable In the present case the data input comes directly from the interface as the Digit value in one byte The number of D Latches must be equal to the number of digits used for the secret code 3 in the present case There is a specific clock for each of the 3 D Latches controlled by the sequencing control module Data can be written Clock activated into a D Latch only if the active mode is Secret code entry and if the re ceived bit corresponds to this location Figure 4 Practically the clock is generated through an AND func tion between the Secret code entr
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7. y mode and the ranking of the received digit This ranking is issued by the counter used for the serial flow reception Figure 4 Digit storage into EEPROM memory Digit Value To 2nd and 3rd EEPROM storage Secret Code _ Entry 1st_Digit EEPROM 4 7 Coded lock using the ST6 REALIZER 2 1 3 Access code entry and recognition The digits are received serially as in the Secret code entry mode and stored in Volatile Memory locations RAM The RAM location are described with standard D Latch symbols The Input Output of this compo nent are exactly the same as for the Non Volatile one allowing a clear analogy between the functional de scription of the two modules The data input channel is the same while the clocks are logically always val idated except if the Secret code entry mode is activated Figure 5 Figure 5 Digits management for code recognition Digit Value To 2nd and 3rd digit stage Secret Code _ Entry 1st_Digit The code recognition is performed by comparison one to one between the values stored in EEPROM and RAM 5 7 Coded lock using the ST6 REALIZER 3 REVISION HISTORY Table 1 Revision history Date October 1995 12 June 2008 Revision Description of changes Initial release Logo modified 6 7 Coded lock using the ST6 REALIZER Please Read Carefully Information in this document is provided solely in co
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