Original Address :: https://blog.csdn.net/nibani/article/details/363906
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RFID has been in contact for some time. EPC is now ready to stop and learn a series of standard protocols. Although UHF C1G2 are out, but HF Class1 still the most mature standards. The following is a learning Auto-ID Lab's HF Class1 V1.00 version of feelings and experiences. Mainly communication protocol and air interface part.
EPC HF (13.56MHz) Class 1 compatible with ISO / IEC15693, and has been accepted ISO / IEC18000-3 in.
Protocol
uses time-slicing terminal adaptive acquisition protocol (Slotted Terminating Adaptive Collection).
Tag into the electromagnetic field into the Ready state.
After receiving a Begin Round Reader, if the coding tag and Begin Round the mask does not match, or the tag in the Ready state; if the match proceeds Slotted Read state.
Slotted into the state, tag Slot will calculate a return based on the contents Begin Round and their information. Meanwhile, Slot counter in the tag will be set to zero. When each of the Reader transmits a Slot on the end of the next information Slot Start, Slot counter in the tag is incremented. When the counter and the calculated position of the same Slot, tag information starts to return.
tag return information is detected Reader. If the Reader does not detect the return information indicating that there is no tag, Reader Send Close Slot Sequence, a new start for the tag Slot. tag of the slot counter is incremented. tag still Slotted state. If the Reader detects a return message, indicating the presence of tag. At this time Reader CRC check bits to detect the tag return information is correct, it can be detected by special methods if there is a conflict exists. If there exist or return information is not normal, Reader Send Close Slot Sequence conflict. At the same time, the tag back to the Ready state. If the Reader to return the tag information is detected normally, Reader transmits a Close Slot Sequence, the tag enters Slot Fixed state.
Slot Fixed into the future state for each tag Begin Round (if the mask matches), reply in particular F Slot. The Reader is not treated reply in the F Slot. It follows that state tag into the Slot Fixed Reader will no longer be identified (they have been identified over).
Air interface
. 1 Reader to the Tag
1.1 operating frequency
FC = 7kHz of 13.56 MHz +/-.
1.2 single pulse characteristics
Reader to tag signals using modulation depth is 10% to 30%, the pulse width is 9.44us (fc / 128) single pulse.
1.3 baud
Reader to tag baud rate is 26.48kb / s (fc / 512) . I.e., four pulse width represents a single 'bit.
1.4 communication signal
meter long frame start, short frame start, frame end, binary 0, binary 1, off time slice sequence (close slot sequence) and other signals.
The binary 0 is expressed after a low pulse 9.44us has three consecutive high pulses of 9.44us. 4 9.44us pulse represents one bit. Thus, the baud rate FC / (. 4 * 128) = FC / 512
for 1.5 command communication
with a sequence start command, the command closing time slice, the time slice fixing command, the command completely reset, a write command and the like.
Reader to the Tag 2
2.1 subcarrier frequency
FSC = FC / 32 = 423.75KHz
2.2 reply signal
comprises a frame start signal, the EPC code, the CRC 16, frame end signal.
2.3 reply signal encoding
a logical 0 is 4 cycles subcarrier signals, followed by 4 cycles of the subcarrier signal is not modulated.
4 is a logic 1 unused cycles subcarrier modulated signal, followed by 4 cycles subcarrier signal.
2.4 reply baud
baud rate fb = fc / (32 * ( 4 + 4)) = fc / 256 = 52.969Kb / s. Because the sub-carrier frequency of fc / 32, while the eight subcarrier signals need to represent each bit, and therefore is fc / (32 * 8) = fc / 256.
3 conflict detection
only returned in the same Slot the tag it may conflict.
Conflict illustrates two (or more) tag have at least one different. Ie by a tag is a logic 1, the other tag is a logic 0.
Logic-zero after four cycles the unmodulated subcarrier; logic 1 is the first four cycles the unmodulated subcarrier.
If Reader read by eight subcarrier modulation cycles are, indicating a conflict.
Reader approach is to close the Slot, these two (a plurality) Tag return to the Ready state.
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