EM4056
Arbitration commands
The arbitration mode is a sophisticated command avoiding collisions among transponders. The arbitration method is based
on the method of multiprocessor bus arbitration.
This feature allows the identification of a transponder out of a group, even if they entered the electromagnetic field at the
same time. At each arbitration, the reader detects one address of a new transponder.
The arbitration session starts with a special StartArbitration command. If the RdEn bit of the transponder is « 0 », then the
transponder belongs to the active group. The arbitration commands will only act on the transponders of the active group.
StartArbitration
After the Start bit, the reader sends a command field which indicates the beginning of an arbitration cycle. An 8 bits CRC
block calculated over the StartArbitration command completes this information.
The transponder returns the first BitVal frame corresponding to the LSB of its 32 bits addresses.
Start of arbitration
1 bit
Reader Start
Transponder
4 bits
MSB
Start_Arbit
8 bits
MSB
CRC
1 bit
2 bits
MSB
Start Continue
6 bits
Bit0 Bit0 X X Bit1 Bit1
ta1p
LSB ROM
ta2p
Fig. 17
BitVal Frame
The BitVal frame consists of 6 bits. If the Nth bit of its address is logic « 0 », the transponder sends two « 0 » at the position
Bit0. If the Nth bit of its address is logic « 1 », the transponder sends two « 0 » at the positions Bit1. The bit repetition
increases the transmission reliability.
The response value of the different transponders is coded with the time position of the answer. Therefore no answer
conflicts are generated.
Note: Reception Bit Period is 32 RFclocks for all the arbitration (BitVal frame and CRC).
BitVal frame
BitVal = 0
BitVal = 1
Bit0
Bit0
X
X
Bit1
X
Bit1
X
Å 32 Rf period
Æ
0
0
X
X
X
X
X
X
0
0
Fig. 18
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