EM4022
Anti-collision Protocol Overview
Control ROM Bit definition
The protocols are a collection of simple but fast and
reliable anti-collision protocols. They allow fast reading
of large numbers of transponders simultaneously using a
single reader. It is even possible to identify transponders
with identical codes, thereby making it possible to count
identical items.
Parameter
Fast / Normal
Mode
Value Mode
0
1
0
1
0
1
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
0
1
Normal
Fast
Free-running
GAP detection enabled
GAP disabled (Free-running)
Slow-down
ACK mode
Free-running protocol
Switch-off
The basis of the BTG-Supertag series of protocols is that
transponders transmit their own codes at random times
to a reader. By just listening and recording unique codes
when they are received, the reader can eventually detect
every tag. The reader detects collisions by typically
checking a CRC.
Maximum
initial random
delay
0 (Continuous)
16 bits
64 bits
256 bits
1 kbits
4 kbits
16 kbits
This basic protocol is known as the “Free-running”
protocol. It requires uniquely coded tags. Its main
advantage is that the reader design is simple, and the
spectrum requirement is much less – a very narrow band
is required.
64 kbits
Data rate
64 kbit/s
32 kbit/s
16 kbit/s
8 kbit/s
Figure 10 shows a sequence of three transponders. The
reader starts first to read transponder 1 but during his
data transmission, transponder 3 starts to modulate. In
this case, due to the CRC check no transponder is
detected. A transponder is taken into account, if it
4 kbit/s
2 kbit/s
1 kbit/s
0.5 kbit/s
Encoding
method
Glitch encoding
Manchester encoding
Low frequency GAP detection
High frequency GAP detection
transmits
a
complete data stream without any
disturbance
GAP type
Control ROM Map
15
14
13
12
11
10
HF
9
8
7
6
5
4
3
2
1
0
Byte[1]
Byte[0]
Random delay
Man-
Data rate
Switch- Free-
off running
Fast
GAP chester
9
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EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
