MAX66120 MAXIM [Maxim Integrated Products], MAX66120 Datasheet - Page 7

• Manufacturer Part Number: MAX66120
• Description: ISO 15693-Compliant 1Kb Memory Fob Powered Entirely Through the RF Field
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 7. Downlink Data Coding (Case “1 Out of 256”)
The path from master to slave uses amplitude modula-
tion (Figure 6); the modulation index can be either in
the range of 10% to 30% or 100% (ISO 15693-2,
Section 7.1). The standard defines two pulse-position
coding schemes that must be supported by a compli-
ant device. Scheme A uses the “1 out of 256” method
(Figure 7), where the transmission of 1 byte takes
4.833ms, equivalent to a data rate of 1655bps. The
location of a modulation notch during the 4.833ms con-
veys the value of the byte. Scheme B uses the “1 out
of 4” method (Figure 8), where the transmission of 2
bits takes 75.52µs, equivalent to a data rate of
26,484bps. The location of a modulation notch during
the 75.52µs conveys the value of the 2 bits. A byte is
transmitted as a concatenation of four 2-bit transmis-
sions, with the least significant 2 bits of the byte being
transmitted first. The transmission of the SOF pattern
takes the same time as transmitting 2 bits in Scheme B.
The SOF pattern has two modulation notches, which
makes it distinct from any 2-bit pattern. The position of
the second notch tells whether the frame uses the
“1 out of 256” or “1 out of 4” coding scheme (Figures 9
and 10, respectively). The transmission of the EOF pat-
tern takes 37.76µs; the EOF is the same for both coding
schemes and has one modulation notch (Figure 11).
The path from slave to master uses one or two subcarri-
ers, as specified by the Subcarrier_flag bit in the request
data packet. The standard defines two data rates for the
response, low (approximately 6600bps) and high
(approximately 26,500bps). The Data_rate_flag bit in the
MODULATED
CARRIER
PULSE-
0 1 2 3 4
_______________________________________________________________________________________
ISO 15693-Compliant 1Kb Memory Fob
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2
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~ 9.44μs
~ 18.88μs
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~ 4.833ms
request data packet specifies the response data rate.
The data rate varies slightly depending on the use of
one or two subcarriers. The LSb is transmitted first. A
compliant device must support both subcarrier modes
and data rates.
In the single subcarrier case, the subcarrier frequency
is 423.75kHz. One bit is transmitted in 37.76µs (high
data rate) or 151µs (low data rate). The modulation is
the on/off key. For a logic 0, the subcarrier is on during
the first half of the bit transmission time and off for the
second half. For a logic 1, the subcarrier is off during
the first half of the bit transmission time and on for the
second half. See Figure 12 for more details.
In the two subcarrier cases, the subcarrier frequencies
are 423.75kHz and 484.28kHz. The bit duration is the
same as in the single subcarrier case. The modulation
is equivalent to binary FM. For a logic 0, the lower sub-
carrier is on during the first half of the bit transmission
time, switching to the higher subcarrier for the second
half. For a logic 1, the higher subcarrier is on during the
first half of the bit transmission time, switching to the
lower subcarrier for the second half. See Figure 13 for
details. The transmission of the SOF pattern takes the
same time as transmitting 4 bits (approximately 151µs
at a high data rate or approximately 604µs at a low data
rate). The SOF is distinct from any 4-bit data sequence.
The EOF pattern is equivalent to a SOF being transmit-
ted backwards. The exact duration of the SOF and EOF
varies slightly depending on the use of one or two sub-
carriers (see Figures 14 and 15, respectively).
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