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T5557 Read/Write RFID Transponder

The Atmel T5557 is a 330 bit Read/Write RFID transponder operating in the 125Khz band. Its memory is
structured in 10 blocks of 33 bits, however only 224 bits are available for storage and retrieval of user defined
data. This is structured as 7 blocks of 32 bits of read/write data. Among the many functions available the T5557
RFID transponder is capable of :
  • Selectable data rates  RF/2 to RF/64
  • Selectable Modulation Encoding.  Manchester,  FSK, PSK, Biphase, NRZ.
  • Maximum block feature.
  • Password protected Read and Write
  • Direct access block read and write.

Reading a T5557 RFID Transponder.

The memory structure of the T5557 transponder is shown here.

b32 b31                               b0
page lock bit data block address
L Configuration Data Block 0
L 32 bits Read / Write data Block 1
page 0 L 32 bits Read / Write data Block 2
L 32 bits Read / Write data Block 3
L 32 bits Read / Write data Block 4
L 32 bits Read / Write data Block 5
L 32 bits Read / Write data Block 6
L User Data or password. Block 7
page 1 1 Traceability Data Block 1
1 Traceability Data Block 2

When the Tag enters the electromagnetic field transmitted by the RFID reader it draws power from the field
and  will commence transmitting its data if so configured.  How the T5557 will respond upon entering the  RF
field is dependent on the data stored in the Configuration block at block address 0.
Block 0, Configuration data.
 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
L 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 1 1 1 0 1 0 0 0
master code Bit rate Encoding psk
Max Block P

The configuration block bits are described in detail in Atmels T5557 datasheet, see T5557 datasheet. Here is
a description of some of the more important configuration bit details.

Bits 16 - 20:  Determine the Encoding protocol upon start up.
                       A bit pattern of 10000 selects Manchester Encoding. When data is transmitted from tag to reader
                       the data is encoding using this selected scheme. See  Data modulation

Bits 12 - 14:  Determine the Bit rate of the data transmitted by the transponder to the reader.
                       A bit pattern of 101 selects a bit rate of 64 Field Cycles per bit.

Bits 25 - 27:  Determine the maximum block address transmitted in standard read mode.
                       For the T5557 RFID transponder this value can be from 0 to 7.

Bit  28:           When Set this bit activates the Password  mode.
                       In Password mode all blocks need a password to be sent before they can be read or written.
                       The password required is stored in block 7.

Bit 0:              Setting Bit 0 to logic 1 will prevent any further writes of the selected block. 
                       This function is used to prevent accidental writes of the data, effectively making it OTP memory.

In addition to the 7 user defined blocks, the T5557 rfid transponder also has two blocks of Traceability data
located in page 1. This information is not alterable and contains manufacturer codes, lot numbers, and other
such data for tracing the source of the transponder.

T5557 Transponder power up sequence.
When the tag enters the RF field and powers up it loads the information stored in the configuration block.
This tells it what bit rate and encoding scheme to transmit in. It then enters into Regular Read Mode.

In Regular Read Mode the tag will start to transmit its data starting from Block 1, and ending in the block
number selected by the Max Block bits of the configuration register. After transmission of all the blocks it 
will continue to retransmit the data starting from block 1 again until a command is sent to it, or it leaves the
RF field.
Often the beginning of each transmission is preceeded with a special terminator sequence that allows the
rfid reader to syncronize to the first block sent. This terminator sequence can be activated by setting bit 29 of
the configuration block.
For a manchester encoded data stream the sequence terminator is defined by a 1 bit, followed by no
modulation for 1 bit length, then another 1 bit, then no modulation for another bit length, as shown here.
T5557 rfid sequence terminator

So when transmitting in Standard read mode with a terminator active and Max Block set to 4 the data blocks
appear as such.

ST Block1 Block 2 Block 3 Block 4 ST Block 1 Block 2 Block 3 Block 4

If the Password mode is active care must be taken to not select a Max Block value of 7 as this will transmit
the password stored in block 7. If a Max Block value of 0 is selected then the configuration block is transmitted

Sending Read and Write Commands.
RFID readers can send commands and data to the T5557 by interrupting the RF Field in a fixed manner.
All commands to the transponder are initiated by producing a "Start gap". To produce the Start gap the RFID 
reader will turn off the field for a period of between 10-50 field cycles. Then to send either 1 or 0 bits the RF field 
is turned on again for a period that varies depending on which bit is being transmitted. With a 1 bit the field will
be active for a period between 48 to 63 field cycles, while for a 0 bit the field will be active for a period between
16 to 31 field cycles. Between each bit the RF field is turned off for a period known as the Write Gap, which is
typically between 8 to 30 field cycles in duration.

Each command to the RFID transponder is fashioned by arranging the 1 and 0 bits as described in the protocol
for the T5557. Shown here is a sub set of the available commands.

1p 0 2   Addr     0 Read selected Block

To send a read block command a logic 1 is sent, followed by the page value bit (0 for page 0), a 0 bit, and
the 3 address bits corresponding to the block addresss of the block required to be read. If the command is
understood by the T5557 transponder it will start to transmit the required block in a continuous loop. If the ST bit
is set in the configuration block then this will be accompanied by the Sequence terminator pattern. Similarily
other commands can be sent as shown here.

1p 0 1   Password    32 2   Addr     0   Read Password Protected Block  

Here, if the PWD bit is set in the configuration block, the password stored in Block 7 must also be sent to read
the required block.

1p L 1     32bit Data     32 2   Addr     0   Standard Write Block  

1p 1    Password   32 L 1     32bit Data     32 2   Addr     0   Protected Write Block  

Here we have a standard Write and a Protected Write to a block. The Protected Write commands require
the password to be sent along with the relevant data. Also the Lock bit  (L) is sent. A 0 bit will allow the block
to be rewritten, while a 1 bit will turn this block into a Read Only location, where no further writes are permitted.

Priority 1 Design carries a stock of low cost T5557 rfid Transponders. You can buy T5557 tags direct from
our online shopfront. Our RFIDREAD-RW  RFID Reader Writer is designed to read T5557 transponders, as
well as the more common EM4100 transponders.  See
RFID Reader and Writer Modules to view our range
of low cost RFID Reader and Writer modules.
    See transponder Specifications.

    RFID keytag 125Khz EM4100 compatible       125khz RFID proximity card  
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