Rainbow Electronics MAX66040 - Manual (Page 7)

The path from slave to master uses an 847.5kHz sub-
carrier, which is modulated using binary phase-shift key
(BPSK) modulation. Depending on the data rate, the
transmission of a single bit takes 8, 4, 2 or 1 subcarrier
cycles. The slave generates the subcarrier only when
needed; i.e., starting shortly before an SOF and ending
shortly after an EOF. The standard defines the phase of
the subcarrier before the SOF as 0° reference, which corresponds to logic 1. The phase of the subcarrier
changes by 180° whenever there is a binary transition
in the character to be transmitted (Figure 9). The first
phase transition represents a change from logic 1 to
logic 0, which coincides with the beginning of the SOF.
The BPSK modulated subcarrier is used to modulate
the load on the device’s antenna (Figure 10).
MAX66040
DATA TO BE TRANSMITTED
INDICATES 180 ° PHASE CHANGE (POLARITY REVERSAL)
OR
1 1 0
847kHz SUBCARRIER
BPSK MODULATION
TRANSMISSION OF A SINGLE BIT
POWER-UP DEFAULT = EIGHT CYCLES OF 847kHz (9.44 μs)
CAN BE REDUCED TO FOUR, TWO, OR ONE SUBCARRIER CYCLES FOR COMMUNICATION IN THE ACTIVE STATE.
Figure 9. Uplink: BPSK Modulation of the 847.5kHz Subcarrier
TRANSMISSION OF A SINGLE BIT
SHOWN AS EIGHT CYCLES OF THE 847kHz SUBCARRIER
DATA*
*DEPENDING ON THE INITIAL PHASE, THE DATA POLARITY MAY BE INVERSE.
1 0 1
Figure 10. Uplink: Load Modulation of the RF Field by the BPSK Modulated Subcarrier
ISO/IEC 14443 Type B-Compliant
Secure Memory
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ABRIDGED DATA SHEET