EM4170
the Acknowledge (ACK) indicating proper communication and end of EEPROM write, and the No Acknowledge (NAK)
when something is wrong.
LIW
ACK
NAK
16 16
64
32
32
16 16
48
16
48
16
16 16
48
16
32
16 16
All numbers represent number of periods of RF field
Fig. 16 a
Fig. 16 b
Fig. 16 c
Communication from the Transceiver to the Transponder (RECEIVE MODE)
The EM4170 can be switched to the Receive Mode ONLY DURING A LISTEN WINDOW. The Transceiver is synchronised
with the incoming data from the transponder. During the phase when the chip has its modulator "ON" (32 periods of RF),
the transceiver has to send a bit "0". At reception of the first "0", the chip stops immediately the LIW sequence and expects
then another bit "0" to switch to receive mode. The transceiver and the chip are now synchronised and further data is sent
with a bit rate of 32 periods of the RF field.
The EM4170 turns "ON" its modulator at the beginning of each frame of 32 clock periods corresponding to one bit. To send
a logic "1" bit, the transceiver continues to send clocks without modulation. After 16 clocks, the modulation device of the
EM4170 is turned "OFF" allowing recharge of the internal supply capacitor. To send a logic "0" bit, the transceiver stops
sending clocks (100% modulation) during the first half of a bit period (first 16 periods). The transceiver must not turn "OFF"
the field earlier than clock 1 of a bit period. It is recommended to turn "OFF" the field after 4 clocks of the bit period. The
field is stopped from clock 5 to 16 of the bit period, and then turned "ON" again for the remaining 16 periods.
To ensure synchronisation between the transceiver and the transponder, a logic bit set to "0" has to be transmitted at
regular intervals. The RM pattern consists of two bits set to "0" thus allowing initial synchronisation.
While the transceiver is sending data to the transponder, two different modulations will be observed on both coils. During
the first 16 clocks of a bit period, the EM4170 is switching "ON" its modulation device causing a modulation of the RF field.
This modulation can also be observed on the transceiver's coil. The transceiver to send a bit "0" will switch "OFF" the field,
and this 100% modulation will be observed on the transponder coil.
11
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