ST25R3918 datasheet(52/141 Pages) STMICROELECTRONICS

52 / 141 page

Application information

ST25R3918

52/141

DS13490 Rev 2

Direct command mode

After the I2C slave address the mode byte to trigger a direct command is sent. As for SPI

some direct commands take some time to execute and no I2C access to the ST25R3918

must be performed until the execution of the direct command is completed. All such direct

commands send an interrupt upon completion to notify the MCU that the I2C bus can be

used again.

Figure 22. Sending a direct command

I2C access to register space-B

To access the register space-B, byte FBh has to be inserted between the I2C slave address

and the register read or write mode byte. Access to register space-B remains active until an

I2C Stop Condition is received.

I2C: transition to and termination of the Transparent mode

When the transparent mode command is received via I2C, the chip interface lines are

switched to the Analogue front end as described in Section 4.4.13: Transparent mode.

Once in transparent mode the BSS signal is used to distinguish between I2C

communication and transparent mode data as follows:

the BSS line must be set high before entering the transparent mode, and then kept high

during the Transparent mode

the Transparent mode is terminated when the BSS line is set to low, followed by at

least one SCL clock pulse

after the termination of the transparent mode the I2C interface can be used again.

MS51658V1

SCL

SDA

Slave address

Direct command byte

Figure 23. Read and Write mode for register space-B access

Write to register space B

Slave

address W

AFBh

address

A Data 0 A Data 1 A

...

Data N

Read from register space B

Slave

address W

AFBh

address

ASr

Slave

address R

A Data 0

Data 1 A

...

Data N N P

Legend: S: Start, Sr: repeated Start, A: ACK, N: NAK, P: Stop.

ST25R3918 Datasheet(PDF) 52 Page - STMicroelectronics

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