EM4056
ReadRom
A ReadRomEn command enables only transponders in the field with RdEn bit set to « 0 » to answer.
With this command, the address of a single new tag entered in the field can be detected because all known transponders
are not allowed to answer if they are deactivated by the RdEn bit (RdEn=1). If more than one transponder answer a CRC
error will be detected and it becomes necessary to perform an arbitration to find all new transponder addresses.
The command is faster than a full arbitration cycle for new tags.
The ReadRomEn command frame consists of three blocks and has a constant length of 13 bits.
The Start bit allows the transponder to synchronise to the new command frame. After the Start bit, the frame contains four
bits for the Command. A CRC block of 8 bits is calculated over the Command and appended to the end.
The transponder frame has a length of 40 bits and starts with the 32 bits ROM block. A CRC block of 8 bits is calculated
over the transponder address (ROM) and appended to the end.
1 bit
Reader
Start
4 bits
MSB
ReadRom
8 bits
X8
CRC
32 bits
MSB
ROM
8 bits
X8
CRC
Fig. 6
Transponder
tsp
SelToggle
A SelToggle command addresses a transponder and toggles the RdEn bit (0→1 or 1→0). The transponder returns a frame
with the changed value of RdEn bit followed by a CRC.
The SelToggle command frame consists of four blocks and has a constant length of 45 bits.
The Start bit allows the transponder to synchronise to the new command frame. After the Start bit the frame contains four
bits for the Command. Next to the Command, a sequence of 32 bits follows with the transponder address. A CRC block of 8
bits is calculated over the Command and the transponder address and appended to the end.
The transponder frame has a length of 10 bits and starts with the RdEn bit and the "not RdEn" bit. A CRC block of 8 bits is
calculated over the RdEn and the "not RdEn" and appended to the end.
1 bit
Reader
Start
4 bits
MSB
SelToggle
32 bits
MSB
ROM
8 bits
X8
CRC
2 bits
8 bits
X8
CRC
Fig. 7
Transponder
tsp
RdEn nRdEn
SelTag
The SelTag command address a transponder with its 32 bit address (ROM) and set the flag Select to 1. After this command,
the selected transponder can answer to commands : Read, Write, Prot, Add, Comp and Login.
1 bit
Reader
Start
4 bits
MSB
SelTag
32 bits
MSB
ROM
8 bits
X8
CRC
2 bits
8 bits
X8
CRC
Fig. 8
Transponder
tsp
Sel nSel
Copyright
©
2005, EM Microelectronic-Marin SA
6
www.emmicroelectronic.com
EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
