ST95HF datasheet(16/93 Pages) STMICROELECTRONICS

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Communication protocols

ST95HF

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DocID025630 Rev 4

Figure 8. Reading data from ST95HF

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 ST95HF, 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 ST95HF 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

ST95HF 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 ST95HF 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 ST95HF is ready.

Note that at the beginning of communication, the application does not need to check flags to

start transmission. The ST95HF is assumed to be ready to receive a command from the

application.

Figure 9. Reset the ST95HF

To reset the ST95HF 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

ST95HF into Power-up state. The ST95HF will wake up when pin IRQ_IN goes low. The

ST95HF reset process only starts when the SPI_SS pin returns to high level.

Table 5. Interpretation of flags

Bit

Meaning (application point of view)

[7:4]

Not significant

Data can be read from the ST95HF when set.

Data can be sent to the ST95HF when set.

[1:0]

Not significant

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

Control Byte

MISO

X X X X X X X X

Resp Code

LEN

DATA

Several data bytes

MOSI

0 0 0 0 0 0 0 1

Control Byte 01

MISO

X X X X X X X X

ST95HF Datasheet(PDF) 16 Page - STMicroelectronics

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