BasicCards 101 (Part 2)
Contents
1. direct in and out instructions Now it s important that the device manufacturer supplies APIs that allow these compil ers to easily interface to the device ZeitControl certainly has taken care of this aspect and it provides an extreme ly inexpensive development kit For BASCOM AVR users the necessary BasicCard drivers exist as well So there s really no reason not to give this a try if you have an application in need of a secure smartcard li Brian Millier is an instrumentation engineer in the Chemistry Department at Dalhousie University in Halifax Canada He also runs Computer Interface Consultants You may reach him at brian millier dal ca PROJECT FILES To download the code go to ftp circuitcellar com pub Circuit_ Cellar 2004 165 SOURCES C702 10M008 2834 Acceptor Amphenol Tuchel 734 451 6400 www amphenol tuchel com AT90S8535 Microcontroller AVR assembler and simulator Atmel Corp 714 282 8080 www atmel com 9088535 Development board Futurlec www futurlec com Series 88 keypad Grayhill Inc 408 354 1040 www grayhill com BASCOM AVR Compiler program mer BasicCard driver library MCS Electronics Holland 31 75 6148799 www incselec com BasicCard ZeitControl Cardsystems 49 0 571 50522 0 www zeitcontrol de www circuitcellar com2. set the value of these vari ables yourself within your BasicCard program should your code encounter an error condition In most designs the card in socket switch will notify the program if the card is removed during use but if an actual data transaction is in progress when this happens the BasicCard driver within BASCOM may hang the program until a time out interval passes Depending on a number of variables this might take up to a minute so beware of this during debugging Before trying your own Basic Card program I recommend that you load the sample Becard bas program into your AVR MCU program a BasicCard with the Calc demo program provided with the development kit and try that combination If everything is satisfac tory you will see the results of the communication between the two devices You can then enter some numbers into your AVR MCU and let the BasicCard act as a calculator CARD FIRMWARE Table 1 shows a list of the commands that I ve defined in the BasicCard for this application The last column in this table indicates where the com mand is used The LN Dispenser is labeled AVR The PC application personalizes the card and later reads the accumulated total usage labeled PC The balance reader is the little key fob device that comes with the development kit STATUS WINDOW www circuitcellar com NAME ACCT OK i LN2 Card ISSUING wa LN2 DISPENSER CARD ISSUE CARD PROGR
3. AM Client Using BM generated DES Encryption key Brian Millier 2933 Last Transaction e LITERS Cancel Last Transaction Set Values Photo 2 This is a screen shot of the PC application that initially person alizes the BasicCard and reads out its balance periodically The PersonalizeCard command which the PC application uses to ini tialize the card with user information and zero out the balance is the only command that requires encryption in order to work This guards against the possibility of fraudulent card produc tion ZeitControl s Visual Basic API which is part of the development kit software includes support for encryp tion This command is only used by the PC program that personalizes the cards and that is written in Visual Basic Although not a concern in this application the fact that the BAS COM AVR BasicCard library does not currently support encryption could be a disadvantage in other applications For this application I used the BasicCard ZC3 9 enhanced card because it was included with the development kit However the lesser models of the card would work as well because this is a simple application In the first part of this series I gave you some hints on how to program the BasicCards by supplementing the instructions in the user manual AVR FIRMWARE Next I ll describe the program that runs on the 8535 which controls the LN dispenser After some initialization of the p
4. CIRCUIT CELLAR THE MAGAZINE FOR COMPUTER APPLICATIONS FEATURE ARTICLE BasicCards 101 Part 2 Use in a Liquid Nitrogen Monitor Circuit Cellar the Magazine for Computer Applications Reprinted by permission For subscription information call 860 875 2199 or www circuitcellar com Entire contents copyright 2001 Circuit Cellar Inc All rights reserved by Brian Millier Now that you re familiar with ZeitControl s BasicCard it s time to take a closer look at the process of programming one and incorporating it in a design Brian shows you how he inte grated BasicCard technology in the design of a liquid nitrogen generator Last month I introduced you to ZeitControl s BasicCard which is a smartcard that is programmed in BASIC In Part 2 I d like to further explore the programming of these cards and discuss a project I built a device that allows you to use BasicCards like debit cards to con trol the dispensing of liquid from a liq uid nitrogen generator storage tank The idea is to issue each liquid nitro gen user here at Dalhousie University with a BasicCard Each card is person alized by entering the user s name account number and a zero balance Card personalization is done on a PC using a Windows based application This user friendly application inter faces to the BasicCard using the CyberMouse reader that comes with the development kit To access some liquid nitro gen LN insert your BasicCard
5. Increase balance by amount dispensed AVR Read name account number and balance AVR and PC AVR Needed by previous command AVR PRDisplay Display information on key fob balance reader Balance reader Table 1 These six commands are implemented in the BasicCard for this application As you can see some com mands are used by both the LN dispensing controller and the PC application that personalizes and reads the cards support for interfacing them to MCUs apart from providing a technical refer ence document describing the ISO IEC 7816 3 standard that the cards use for communication From what I could see it would have been quite time con suming to personally write a suitable driver to allow AVR MCUs to talk to BasicCards As luck would have it the developer of the BASCOM AVR compil er the language I use exclusively for all of my AVR based projects had a beta version of a driver library available This was one of those good news bad news situations I was able to get the library free from the developer but I was at that time the first and only beta tester I ended up figuring out on my own some of the patches needed to make it work To interface a BasicCard to an AVR MCU using the BASCOM compiler you must run BASCOM version 1 11 6 8 or newer You must also load the BasicCard library available from MCS into BASCOM s LIB folder Next within your BASCOM program you must do the following four things First use the C
6. ONFIG BCCARD command to tell the driver which port pins you have connected your BasicCard socket to This is simple because you only have to tell it which port you are using and to which pins the RESET and I O lines are connected This is clearly described in the documentation that comes with the library Second you must declare each of your BasicCard commands to the BAS COM program using the BCDEF com mand Because you have already written the BASIC code that runs in the BasicCard you will have already defined the commands that the BasicCard recog nizes These command names followed by their parameter lists are used with the BCDEF command Next instruct the compiler to use CIRCUIT CELLAR the proper data rate Use the BAUD 9600 and the Crystal 3579000 directives Finally issue a BCRESET command to initialize the BasicCard as soon as you see that a card has been inserted into the card socket After this preparation initialization all you have to do to access a particu lar command in the BasicCard is use the BCCALL procedure This is similar to any BASIC procedure except that it includes some BasicCard specific parameters The following is the syn tax for this command BCCALL name nad cla ins pl p2 Cparaml paramn where name is the name of the proce dure in the BasicCard to call It must be defined first with BCDEF The name used with BCDEF and BCCALL does not need to be the same as the procedur
7. e in the BasicCard because the CLA and INS bytes actually tell the BasicCard which command to execute However it makes sense to use the same names for consistency nad is the node address byte Basic Cards respond to all node address val ues zero is used here as a default cla is the class byte It is the first of a 2 byte CLA INS command It must match the value you used for the com mand in the BasicCard program itself ins is the instruction byte It is the second of the 2 byte CLA INS com mand The same consideration applies as for the CLA byte p1 is parameter 1 of the CLA INS header Use a zero for your purposes p2 is parameter 2 of CLA INS header Again use a zero for your purposes param1 through paramn are the parameters you want to pass to the BasicCard as required by the command The BasicCard operating system www circuitcellar com employs a comprehensive error reporting scheme This is neces sary in any device used for com merce particularly in a device that you can pull out of its sock et in the middle of program exe cution Describing the error handling is beyond the scope of this article but I will mention that the BCCARD library sup ports it to some extent In essence if the BasicCard returns an error the library will set the BASIC variable ERR and two sta tus bytes SW1 and SW2 will contain error codes Many of these codes are predefined in the BasicCard protocol but you can also
8. into the custom controller con nected to the LN generator The controller checks to ensure that the card is properly person alized for this use and displays your name account number and the number of liters of LN previously consumed during the current billing period You then enter the amount of LN desired on the controller s keypad After updating the BasicCard EEP ROM variable which stores the accumulated LN usage the controller activates a relay that opens a valve and lets the 24 Issue 165 April 2004 liquid nitrogen flow for a long enough period to dispense the necessary amount of LN Periodically the BasicCards are col lected and another PC application is run that zeroes out the accumulated LN total It transfers that figure to a table that is used for the actual billing process In the past an honor system was used in which users entered their LN usage on a sign out sheet posted next to the generator We lost some LN billings here at the university because of dishonesty and low ball estimates of the actual amounts taken Also there was a significant amount of clerical time spent tally ing all of the entries on the daily sign up sheets COE LAI Photo 1 Check out the monitor before it s mounted in its cabinet Note the BasicCard sticking out of the card socket on the right hand side CIRCUIT CELLAR CIRCUIT DETAILS Because the prototype would be the only unit I would need I wanted to
9. ntly in each case so using an interrupt to signal card in socket status was not ideal for this project The BasicCard interfaces to the 8535 using only two port lines The RESET input to the BasicCard is connected to port D2 and the I O line connects to port D4 As I mentioned earlier the BasicCard gets its clock signal directly from the 8535 s XTALI pin which is its oscillator buffer output Although you have to be careful tapping off a clock signal from an MCU s oscillator output the BasicCard presents in this case such a small load that the oscilla tor is unaffected by its presence The user interface is the standard key pad LCD I had a Grayhill series 88 key pad on hand which contains the num bers in a telephone like arrangement as well as several extra keys labeled Enter Clear etc that provide all the necessary input functions Eight lines are need ed to interface this Matrix key pad and I used port A for that purpose Doing so meant I could not make use of the eight channel ADC contained in the 8535 but I didn t need activate the dispensing valve This was a solenoid valve that required 120 VAC to operate so I decided to use a relay to keep any inductive kickback from its coil away from the MCU circuitry Any relay with a 12 V coil and contacts able to switch 1 A AC will do for K1 If the coil needs more than a few hundred milliamps to operate you ll need a larg er transistor than a 2N3904 f
10. operator for an initial transfer tube chilling time as well as the number of seconds required to transfer 1 liter of LN These param eters are subsequently saved to EEP ROM in the 8535 and used in all future liquid transfers unless the cali bration is changed If you remove the card before enter ing the desired number of liters to dispense the LCD indicates that the card has been removed prematurely and returns to the start of the loop CARD ISSUER PROGRAM Photo 2 shows a screen capture of the Visual Basic Card Issuer applica tion This program is run on a secure PC because it is used to personalize the BasicCard with the username and account number and to set the initial Issue 165 April 2004 27 28 Issue 165 April 2004 balance variable to zero Obviously anyone with access to this program can insert their card and wipe out its balance easily After start up the program waits until a card is inserted It checks that the card has the proper program in it for this application It does this by reading the app icationID variable contained in the card s EEPROM If it matches the program displays the user information and the current bal ance If it s a new card that s been pro grammed with the LN application but not yet personalized it will show blank fields and allow you to enter the applicable name account information and also a balance amount typically zero for a new account There is also a
11. or Q1 Diode D1 is placed across the relay coil to protect Q1 from the spike that occurs when the relay turns off The 5 V power supply regulator is contained on the Futurlec PCB but the power transformer bridge and fil ter capacitor are mounted externally Photo 1 shows the development board with the extra components needed for this project The development board comes with a MAX232 for RS 232 communications purposes Although I did not use this feature it would be easy to wire the controller to a remote PC for example if you want to log all the transactions in real time to a computer file Atmel s AT90S85835 is a versatile MCU In some respects it is overkill for this application With the program written in compiled BASIC much of its 8 KB flash program memory is unused It contains 512 bytes of EEP ROM which is unused apart from a few bytes used to store some valve time calibration parameters The eight channel ADC UART and SPI func tions weren t needed either However the assembled Futurlec development board including the 8535 MCU and programmer cable cost less than 30 so I thought it made a lot of sense to do things this way INTERFACE TO THE AVR MCU Before I ordered the BasicCard development kit I wanted to be sure I could use the cards with my MCU of choice the AVR series from Atmel The BasicCard development kit con tains software to program the cards themselves as well as a few different prog
12. orts the program basically enters a loop The program prompts you to insert the card and then waits for this to happen The ReadCardData command is then issued to the CIRCUIT CELLAR BasicCard 2C3 9 BasicCard and the user infor mation contained in the card is displayed on the LCD You are then prompted to enter the amount of LN needed This amount is first added to the BasicCard s balance variable and then the program waits until you indicate you re ready for the dispensing to start It then activates the relay for the amount of time necessary to dispense the necessary LN This is where calibration is needed When dispensing LN it takes a little while for the transfer tube to become chilled enough to pass the liquid Thereafter the liquid flows steadily with the amount dis pensed being proportional to the time the valve remains open After this amount of time the program waits until the card is removed and then goes back to the start of the loop Calibration involves determining the initial chill time and the time liter parameters empirically and storing them as calibration parameters It s important that this calibration can be done in a way that s both con venient for the operator of the genera tor and secure from tampering To that end I designed the program so that when it sees a card with an account number equal to zero the operator account it goes into a calibration rou tine and prompts the
13. provision to cancel the last transaction The amount of the last transaction is shown and there is a button to subtract this amount from the accumulated total The purpose of this function is to allow the operator of the machine to cancel a transaction if the machine fails to deliver LN as requested i e the tank is empty or a valve sticks I also included a box that displays the type of card that has been inserted into the reader This card specific information is returned by all smart cards as part of the answer to reset ATR routine which is invoked at card insertion GIVE IT A TRY I must admit that I was intrigued by the fact that these tiny BasicCards contain more resources except for I O than the typical MCUs I routinely use Furthermore all of this capability is sandwiched into the small area under the gold contact pad The rest of the card is just plastic filler to make the card easy to handle I am definitely in the compiler camp and generally avoid MCUs like BASIC Stamps which run as inter preters However for this purpose I have to admit that the BasicCard interpreter design is quite useful I suspect that many readers like myself are not quite up to the task of designing their own device drivers for high level PC languages like Visual Basic running on Windows It was a CIRCUIT CELLAR different story in the past when you could easily design an ISA card plunk it into the PC and access it using
14. rams to develop PC applications However the kit doesn t provide any Grayhill Series 88 an ADC for this project The Futurlec board has a 10 pin header connected to this port which made it easy to connect the keypad using a ribbon cable I didn t need a large LCD because there isn t a lot of information to display Therefore I used a 2 x 16 dis play and connected it to the 8535 in 4 bit mode using six lines of port C The Futurlec board also provides a 14 pin header for the LCD with all the signal and power wiring taken care of as well as POT1 for contrast adjustment Apart from wiring a few lines to the smartcard socket all the circuitry I needed to add was the driver and relay to www circuitcellar com AT90S8535 Card inserted switch S1 Open with card in place BasicCard socket Amphenol C702 10M008 2834 1N4004 C1 470u 25V CIRCUIT CELLAR K1 Relay SPST Line 7 H tv VY Neutral Figure 1 The liquid nitrogen dispensing monitor was built on a Futurlec 8535 development board Apart from the card socket keypad LCD and relay driver most of the circuitry already exists on the development board Issue 165 April 2004 25 26 Issue 165 April 2004 Command Name Description PersonalizeCard IncreaseAmount GetCardData CancelLastTransaction Self explanatory ReadLastTransaction Used by Initial card with name account number and balance PC
15. use a commercial development board and just add the few custom parts needed for the design I chose the Futurlec 8535 development PCB because it s inexpensive contains headers for commonly used peripher als and has a large enough prototype area to mount the few extra compo nents I needed to complete the design Figure 1 is a diagram of the circuit Some of the circuitry on the Futerlec board that is not required for this project is not shown in the diagram For exam ple the in circuit serial programming port for the 8535 s flash program memo ry is not shown There is one small change that I had to make to the Futurlec board itself The board comes fitted with an 8 MHz MCU clock crystal I changed that to 3 579 MHz so that I could use a common clock for both the MCU and BasicCard which has a 5 MHz maximum clock rate and communicates at 9600 bps when clocked at 3 579 MHz I mounted an Amphenol C702 10M0008 2834 smartcard socket in the prototype area of the PCB This socket contains an NC switch that opens up when a card is inserted mak ing it easy for the MCU to know when to establish com munications with the card www circuitcellar com Although I connected this line to port D3 of the 8535 INT1 I don t use this pin as an interrupt input instead I poll the pin to see when a card is either inserted or removed There are a few different phases in the program and the removal of a card must be handled differe
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