CR95HF datasheet(13/63 Pages) STMICROELECTRONICS

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CR95HF

Communication protocols

Doc ID 018669 Rev 8

13/63

Figure 10.

Reading data from CR95HF

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 CR95HF, 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 CR95HF 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

CR95HF 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 CR95HF 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 CR95HF is ready.

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

start transmission. The CR95HF is assumed to be ready to receive a command from the

application.

Figure 11.

Reset the CR95HF

To reset the CR95HF using the SPI, the application sends the SPI Reset command (Control

Byte 01, see Figure 11) which starts the internal controller reset process and puts the

CR95HF into Power-up state. The CR95HF will wake up when pin IRQ_IN goes low. The

CR95HF reset process only starts when the SPI_SS pin returns to high level.

Caution:

SPI communication is MSB first.

4.2.2

Interrupt mode

When the CR95HF is configure to use the SPI serial interface, pin IRQ_OUT is used to give

additional information to user. When the CR95HF is ready to send back a reply, it sends an

Interrupt Request by setting a low level on pin IRQ_OUT, which remains low until the host

reads the data.

The application can use the Interrupt mode to skip the polling stage.

Caution:

SPI communication is MSB first.

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

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