Communication to the reader
The card has two ways to send its data back to the reader. Both use a subcarrier transmitted back to the reader using load modulation.
Amplitude-shift keying
Amplitude-shift keying 100% modulation index on a 423.75 kHz subcarrier. The data rate can be:
- Low 6.62 kbit/s (fc/2048)
- High 26.48 kbit/s (fc/512)
A logic 0 starts with eight pulses of 423.75 kHz followed by an unmodulated time of 18.88 μs (256/ fc); a logic 1 is the other way round. The data frame delimiters are code violations, a start of frame is:
- an unmodulated time of 56.64 μs (768/ fc),
- 24 pulses of 423.75 kHz
- a logic 1
and the end of a frame is:
- a logic 0
- 24 pulses of 423.75 kHz
- an unmodulated time of 56.64 μs
The data are sent using a Manchester code.
Frequency-shift keying
Frequency-shift keying by switching between a 423.75 kHz sub carrier (operating frequency divided by 32) and a 484.25 kHz sub carrier (operating frequency divided by 28). The data rate can be:
- Low 6.67 kbit/s (fc/2032)
- High 26.69 kbit/s (fc/508)
A logic 0 starts with eight pulses of 423.75 kHz followed by nine pulses of 484.28 kHz; a logic 1 is the other way round. The data frame delimiters are code violations, a start of frame is:
- 27 pulses of 484.28 kHz
- 24 pulses of 423.75 kHz
- a logic 1
and the end of a frame is:
- a logic 0
- 24 pulses of 423.75 kHz
- 27 pulses of 484.28 kHz
The data are sent using a Manchester code.
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