ST25R95 datasheet(9/61 Pages) STMICROELECTRONICS

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Communication protocols

4.1

Serial peripheral interface (SPI)

4.1.1

Polling mode

To send commands and receive replies, the application software has to perform three steps.

Send the command to the ST25R95.

Poll the ST25R95 until it is ready to transmit the response.

Read the response.

After a command, the application software needs to wait for the ST25R95 to be ready to send the response. Not

following this procedure may cause unpredictable behaviour.

The maximum allowed SPI communication speed is fSCK. The ST25R95 supports SPI communication configured

for CPOL = CPHA = 1 and SPI communication configured for CPOL = CPHA = 0.

A control byte is used to specify a communication type and direction:

•

0x00: Send command to the ST25R95

•

0x03: Poll the ST25R95

•

0x02: Read data from the ST25R95

•

0x01: Reset the ST25R95

The SPI_SS line is used to select a device on the common SPI bus. The SPI_SS pin is active low.

When the SPI_SS line is inactive, all data sent by the Master device is ignored and the MISO line remains in High

Impedance state.

In Slave mode, the phase and polarization are defined with CPOL = 1 and CPHA = 1 or CPOL = 0 and CPHA = 0.

Figure 6. Sending command to ST25R95

MOSI

0 0 0 0 0 0 0 0

CMD

LEN

DATA

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

Figure 7. Polling the ST25R95 until it is ready

MOSI

0 0 0 0 0 0 1 1

Control Byte

MISO

Flag

0 0 0 0 0 X X X

X X X X X X 1 1

X X X X X X X X

0 0 0 0 0 X X X 0 0 0 0 1 X X X

Flag

Flags are polled until data is ready (Bit 3 is set when data is ready)

ST25R95

Communication protocols

DS12807 - Rev 4

page 9/61

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