ST25R3920 datasheet(46/152 Pages) STMICROELECTRONICS

46 / 152 page

Application information

ST25R3920

46/152

DS13261 Rev 9

MISO pin is updated on the rising edge of the SCLK signal. Data are transferred byte-wise,

most significant bit first. Read and Write commands support an address auto increment to

reduce communication time. Table 8 provides an overview of the SPI signals.

The MISO output is in tristate as long as no output data is available. Due to this the MOSI

and the MISO can be externally shorted to create a three-wire SPI. During the time the

MISO output is in tristate, it is also possible to switch on a 10 kΩ pull down by activating

option bits miso_pd1 and miso_pd2 in the IO configuration register 2.

Figure 10. Exchange of signals with a microcontroller

The first two bits of the first byte transmitted after the BSS high to low transition define the

SPI operation mode. All Read and Write modes support address auto incrementing, which

means that if, after the address and first data byte some additional data bytes are sent (or

read), they are written to (or read from) addresses incremented by 1.

Table 9 shows available SPI operation modes. Register read and write operations are

possible in all ST25R3920 operation modes. FIFO and PT_memory operations are possible

in case en (bit 7 of the Operation control register) is set and the crystal oscillator is stable.

Some direct commands are accepted in all operation modes, others require en (bit 7 of the

Operation control register) to be set and the crystal oscillator to be stable (see Table 11).

Table 8. Serial data interface (4-wire interface) signal lines

Name

Signal

Signal level

Description

I2C_EN

Digital input

CMOS

Pull to GND for SPI operation

BSS

Digital input

Active low - Slave select

MOSI

Digital input

Master out - Slave in (MCU → ST25R3920)

MISO

Digital output with tristate

Master in - Slave out (ST25R3920 → MCU)

SCLK

Digital input

Serial clock

IRQ

Digital output

Active high - Interrupt output pin

MS53529V1

MOSI

MISO

I/O

MOSI

MISO

MOSI

Separate SPI input and

output signals to MCU

Bidirectional data

IO signal to MCU

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