ST95HF datasheet(15/93 Pages) STMICROELECTRONICS

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ST95HF

Communication protocols

4.1

Serial peripheral interface (SPI)

4.1.1

Polling mode

In order to send commands and receive replies, the application software has to perform 3

steps.

Send the command to the ST95HF.

Poll the ST95HF until it is ready to transmit the response.

Read the response.

The application software should never read data from the ST95HF without being sure that

the ST95HF is ready to send the response.

The maximum allowed SPI communication speed is fSCK.

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

•

0x00: Send command to the ST95HF

•

0x03: Poll the ST95HF

•

0x02: Read data from the ST95HF

•

0x01: Reset the ST95HF

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 ST95HF

Figure 7. Polling the ST95HF until it is ready

MOSI

0 0 0 0 0 0 0 0

CMD

LEN

DATA

Control Byte

MISO

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 X X X X X X X X

Several data bytes

MOSI

0 0 0 0 0 0 1 1

X X X X X X 1 1

Control Byte

MISO

X X X X X X X X

Flag

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

0 0 0 0 0 X X X

0 0 0 0 1 X X X

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