P4022 EM Microelectronic, P4022 Datasheet - Page 11

• Manufacturer Part Number: P4022
• Description: Multi Frequency Contactless Identification Device
• Manufacturer: EM Microelectronic

WAKE-UP
An ACK sent after correct receipt of a code is
interpreted by the other transponders in the field
as a WAKE-UP. The ACK arrives synchronously at
the transponder that has just transmitted, but
asynchronously at all the other transponders.
necessary, a WAKE-UP can also be sent if the
code is not received correctly, making sure that it
will not be interpreted as an
transmitting transponder. This could speed up the
protocol, but runs the risk of turning transponders
off by accident.
To detect a WAKE-UP, the chip checks for two
GAPs, less than 7 bits apart and each less than
seven bits wide.
must made
frequencies. To be safely interpreted as a WAKE-
UP, the GAPs should be sent less than 5 bits apart,
and each should be less than 5 bits wide. This
has an implication in the case of the high
frequency ACK, which could theoretically consist
of two very narrow GAPs 6 bits apart. In practice
though, the GAPs will be typically at least one bit
wide, making the separation five bits.
Like the MUTE, the low frequency ACK GAPs
should be at least 1.5 bits wide to serve as a
reliable WAKE-UP.
It should be
recognise WAKE-UPs is not critical. The protocol
might be slowed down marginally, but will still
work, as the chips time-out of the sleep mode
automatically after 128 bits.
for
noted
EM MICROELECTRONIC-MARIN SA
As with the MUTE allowance
the
Figure 7: Data encoding methods
that failure
30%
spread
ACK by the
to
in
reliably
clock
If
Data Encoder
The transmitted code always consists of an 11 bit
preamble followed by the 64 code bits.
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.
The P4022 can be programmed for one of two
data encoding methods. The first method is a
variation on
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.
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.
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.
Manchester II,
P4022
PRELIMINARY
i.e.
a ONE
The
11
is