EM4022
The second encoding method is called GLITCH
encoding. A ONE is represented by a HIGH in the first
quarter of the bit period, while a ZERO is represented by
a HIGH in the third quarter of the bit period.
Data Encoder
The transmitted code always consists of an 11 bit
preamble followed by the 64 code bits. The preamble
consists of 8 start bits (ZEROES), followed by a SYNCH.
The SYNCH consists of a LOW for two bit periods
followed by a ONE.
In GLITCH encoding the longest modulation period is
one quarter of a bit period, compared to the Manchester
encoding, where the longest modulation period is one full
bit period. GLITCH encoding therefore requires a much
smaller power storage capacitor.
The EM4022 can be programmed for one of two data
encoding methods. The first method is a variation on
Manchester II, i.e. a ONE is represented by a HIGH in
the first half of a bit period, and a ZERO is represented
by a LOW in the first half of a bit period.
Data Encoding
"0" "0" "1"
Fig. 8
ROM programming
CONTROL ROM
The EM4022 contains three laser fuse ROM blocks that
are pre-programmed by the foundry.
The operational modes of the EM4022 are pre-
programmed into the CONTROL ROM. The contents of
this one is not read out.
CODE ID ROM
This ROM contains the 64 bit ID code. The foundry will
automatically program a unique 48 bit ID and 16 bit
CRC. In this case the most significant bit of the ID is
programmed into bit 0 of the ROM, which will be
transmitted first.
CRC Block Diagram
Data Input
15
14 13 12 11 10 9 8 7 6 5 4 3 2
1 0
LSB
X0
MSB
X15
X2
Feedback before shift
Exclusive OR
Shift Register
X
CRC-CCITT Generating polynomial = X15 + X2 + X0
Fig.9
8
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