How to write selectively to an RFID tag?

Question

How can I efficiently write to an RFID tag without using a For loop. Right now I am looping and filling up all the blocks in the series. I want to make a program were I could fill in specific blocks with specific values. I want to know if there are other ways writing on RFID. The code below shows writing on RFID using the for loop which skips the integers.

Here's my code:

Private Sub RFIDAuth()
    Dim SkipBlock As String
    SkipBlock = ",3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,"
    For i = 1 To 62
        If SkipBlock.Contains("," & CStr(i) & ",") = False Then
            Call ClearBuffers()
            SendBuff(0) = &HFF                      'CLA
            SendBuff(2) = &H0                       'P1: same for all source types
            SendBuff(1) = &H86                      'INS: for stored key input
            SendBuff(3) = &H0                       'P2: for stored key input
            SendBuff(4) = &H5                       'P3: for stored key input
            SendBuff(5) = &H1                       'Byte 1: version number
            SendBuff(6) = &H0                       'Byte 2
            SendBuff(7) = CInt(i)         'Byte 3: sectore no. for stored key input

            SendBuff(8) = &H60                  'Byte 4 : Key A for stored key input
            'SendBuff(8) = &H61                  'Byte 4 : Key B for stored key input
            SendBuff(9) = &H20                  'Byte 5 : Session key for volatile memory
            'SendBuff(9) = CDec(<INPUT>)    'Byte 5 : Session key for non-volatile memory
            SendLen = &HA
            RecvLen = &H2

            retCode = SendAPDUandDisplay(0)
            Base64StrfrmRFID = Base64StrfrmRFID & RFIDRead(i)

        End If
    Next
End Sub

I want to write specific Values for specific blocks in the RFID. — Elwick, Apr 08 '15 at 09:32

score 0 · Accepted Answer · answered Apr 08 '15 at 10:13

SkipBlock: HashSet instead of string

The SkipBlock string and Contains(…) appear strange to me, use a HashSet<int> unless there is a good reason to use the string:

HashSet<int> SkipBlock = new HashSet<int>(){ 3, 7, 11, … };

and later:

if (SkipBlock.Contains(i)) {

Structure for the RFID layout

Use a struct to specify the layout of the RFID:

[StructLayout (LayoutKind.Explicit, Pack=1, Size=…)]
struct RFID_Block {
     [FieldOffset(0)] public const byte CLA = 0xFF;
     [FieldOffset(1)] public const byte INS = 0x86;
     [FieldOffset(2)] public const byte P1 = 0x0;
     …
     [FieldOffset(7)] public int SectorNumber; // Should this be an int or a byte?
};

RFID_Block block1 = new RFID_Block();
block1.SectorNumber = i;
…

Use const for fields that are the same for each block and non-const fields for fields that may vary.
If a field has different meanings in different kinds of RFID blocks, you can define fields with the same FieldOffset, i.e.:
```
struct DualUseRFID_Block {
     …
     // Stored key input block
     [FieldOffset(2)] public byte P2;
     [FieldOffset(3)] public byte P3;

     // Some other kind of RFID Block:
     [FieldOffset(2)] public word FooBar;
```
Note:
- first, FooBar has the same field offset as P2;
- second, FooBar is of a different type than P2; and
- third, FooBar occupies the same memory space as P2 and P3 either FooBar or P2 and P3 contain valid data.
Check the sizes of the fields do not confuse byte and int (4 bytes); i.e. withing an int and then something with an offset of one byte more is asking for problems (e.g. SendBuff(7) = CInt(i): Sendbuf(8) = &H60).
Check whether C# and the RFID chip agree about "endianess".

References

See MSDN about the StructLayout-attribute
See MSDN about using structs
See MSDN Structs tutorial; it includes details about memory layout and that fields in a struct can overlap if you like.

How to write selectively to an RFID tag?

1 Answers1

SkipBlock: HashSet instead of string

Structure for the RFID layout

References