ST25R95 datasheet(10/61 Pages) STMICROELECTRONICS

10 / 61 page

Table 5. Interpretation of flags

Bit

Meaning (application point of view)

[7:4]

Not significant

Data can be read from the ST25R95 when set.

Data can be sent to the ST25R95 when set.

[1:0]

Not significant

Figure 8. Reading data from ST25R95

MOSI

0 0 0 0 0 0 1 0

Control Byte

MISO

X X X X X X X X

Several data bytes

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

Resp code

LEN

DATA

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 ST25R95, 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

ST25R95 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 ST25R95 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 ST25R95 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 ST25R95 is ready. Alternatively the application can also poll the IRQ_OUT pin (see

Section 4.1.2 Interrupt mode).

Note:

At the beginning of communication, the application does not need to check flags to start transmission. The

ST25R95 is assumed to be ready to receive a command from the application.

Figure 9. Reset the ST25R95

MOSI

0 0 0 0 0 0 0 0

Control Byte 01

MISO

X X X X X X X

To reset the ST25R95 using the SPI, the application sends the SPI Reset command (control byte 01, see

Figure 9. Reset the ST25R95) which starts the internal controller reset process and puts the ST25R95 into

Power-up state. The ST25R95 will wake up when pin IRQ_IN goes low. The ST25R95 reset process is delayed

until when the SPI_SS pin returns to high level.

Caution:

SPI communication is MSB first.

ST25R95

Serial peripheral interface (SPI)

DS12807 - Rev 4

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