ST25R3911B datasheet(23/116 Pages) STMICROELECTRONICS

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Figure 14. SPI communication: reading of FIFO

SCLK rising edge

Data transferred from MCU

SCLK falling edge

Data is sampled

/SS raising

edge

indicates

end of

FIFO Mode

10 pattern

indicates

FIFO Mode

tristate

/SS

SCLK

MOSI

MISO

SCLK rising edge

Data moved from FIFO

SCLK falling edge

Data transferred to MCU

1 to 96

bytes

Direct Command Mode

Direct Command Mode has no arguments, so a single byte is sent. SPI operation mode bits 11 indicate Direct

Command Mode. The following six bits define command code, sent MSB to LSB. The command is executed on

falling edge of last clock (see Figure 15).

While execution of some Direct Commands is immediate, there are others that start a process of certain duration

(calibration, measurement…). During execution of such commands it is not allowed to start another activity over

the SPI interface. After execution of such a command is terminated an IRQ is sent.

Figure 15. SPI communication: direct command

SCLK rising edge

Data transferred from MCU

SCLK falling edge

Data is sampled

/SS raising edge

indicates start of

command execution

Two leading 1s

indicate

Command Mode

/SS

SCLK

MOSI

Direct command chaining

As shown in Figure 16, direct commands with immediate execution can be followed by another SPI mode (Read,

Write or FIFO) without deactivating the /SS signal in between.

ST25R3911B

Application information

DS11793 - Rev 6

page 23/116

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