ST25R3911B datasheet(25/116 Pages) STMICROELECTRONICS

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Figure 18. SPI read timing

...

DATAI

...

DATAO

tDOD

tDOHZ

/SS

MOSI

MISO

SCLK

Interrupt interface

There are three interrupt registers implemented in the ST25R3911B: Main interrupt register contains information

about six interrupt sources, while two bits reference to interrupt sources detailed in Timer and NFC interrupt

When an interrupt condition is met the source of interrupt bit is set in the Main interrupt register and the IRQ pin

transitions to high.

Table 8. IRQ output

Name

Signal

Signal level

Description

IRQ

Digital output

CMOS

Interrupt output pin

The microcontroller then reads the Main interrupt register to distinguish between different interrupt sources. The

interrupt registers 0x17, 0x18 and 0x19 are to be read in one attempt. After a particular Interrupt register is read,

its content is reset to 0. Exceptions to this rule are the bits pointing to auxiliary registers. These bits are only

cleared when corresponding auxiliary register is read. IRQ pin transitions to low after the interrupt bit(s) that

caused its transition to high has (have) been read.

Note:

There may be more than one interrupt bit set in case the microcontroller does not immediately read the interrupt

registers after the IRQ signal has been set and another event causing interrupt has occurred. In that case the

IRQ pin transitions to low after the last bit that caused interrupt is read.

If an interrupt from a certain source is not required, it can be disabled by setting corresponding bit in the Mask

Interrupt registers. When masking a given interrupt source the interrupt is not produced, but the source of

interrupt bit is still set in Interrupt registers.

FIFO water level and FIFO status registers

The ST25R3911B contains a 96 byte FIFO. In case of transmitting the Control logic shifts the data that was

previously loaded by the external microcontroller to the Framing Block and further to the transmitter. During

reception, the demodulated data is stored in the FIFO and the external microcontroller can download received

data at a later moment.

ST25R3911B

Application information

DS11793 - Rev 6

page 25/116

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