RX95HF Datasheet, PDF (12/44 Pages) STMicroelectronics – Near field communication transceiver for tag emulation

Communication protocols
RX95HF
Table 5. Interpretation of flags
Bit
Meaning (Application point of view)
[7:4]
Not significant
3
Data can be read from the RX95HF when set.
2
Data can be sent to the RX95HF when set.
[1:0]
Not significant
Figure 8. Reading data from RX95HF
MOSI _{0 0 0 0 0 0 1 0 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X}
MISO
Control Byte
X X X X X X X X Resp Code
LEN
DATA
DATA
Several data bytes
Data must be sampled at the rising edge of the SCK signal.
‘Sending’, ‘Polling’ and ‘Reading’ commands must be separated by a high level of the
SPI_SS line. For example, when the application needs to wait for data from the RX95HF, it
asserts the SPI_SS line low and issues a ‘Polling’ command. Keeping the SPI_SS line low,
the Host can read the Flags Waiting bit which indicates that the RX95HF can be read. Then,
the application has to assert the SPI_SS line high to finish the polling command. The Host
asserts the SPI_SS line low and issues a ‘Reading’ command to read data. When all data is
read, the application asserts the SPI_SS line high.
The application is not obliged to keep reading Flags using the Polling command until the
RX95HF is ready in one command. It can issue as many 'Polling' commands as necessary.
For example, the application asserts SPI_SS low, issues 'Polling' commands and reads
Flags. If the RX95HF is not ready, the application can assert SPI_SS high and continue its
algorithm (measuring temperature, communication with something else). Then, the
application can assert SPI_SS low again and again issue 'Polling' commands, and so on, as
many times as necessary, until the RX95HF is ready.
Note that at the beginning of communication, the application does not need to check flags to
start transmission. The RX95HF is assumed to be ready to receive a command from the
application.
Figure 9. Reset the RX95HF
MOSI _{0 0 0 0 0 0 0 1}
MISO
Control Byte 01
XXXXXXXX
Caution:
To reset the RX95HF using the SPI, the application sends the SPI Reset command (Control
Byte 01, see Figure 9) which starts the internal controller reset process and puts the
RX95HF into Power-up state. The RX95HF will wake up when pin IRQ_IN goes low. The
RX95HF reset process only starts when the SPI_SS pin returns to high level.
SPI communication is MSB first.
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