L99DZ320 datasheet(89/146 Pages) STMICROELECTRONICS

89 / 146 page

To verify, that the SCK Phase of the SPI master is set correctly a special device information register is

implemented. By reading this register the data must be 55 H. In case AAH is read the CPHA setting of the SPI

master is wrong and a proper communication cannot be guaranteed.

CSN timeout

By pulling CSN low the SDO is set active and leaves its tristate condition. To ensure communication between

other SPI devices within the same bus even in case of CSN stuck at low a CSN timeout is implemented. By

pulling CSN low an internal timer is started. After timer end is reached the actual communication is rejected and

the SDO is set to tristate condition.

SDI stuck at GND

As a communication with data all -‘0’ and OpCode ‘00’ on address b’000000 cannot be distinguished between a

valid command and a SDI stuck at GND this communication is not allowed. Nevertheless, in case a stuck at GND

is detected the communication is rejected and the SPIE is set with the next communication.

SDI stuck at HIGH

As a communication with data all -‘1’ and OpCode ‘11’ on address b’111111 cannot be distinguished between a

valid command and a SDI stuck at HIGH this communication is not allowed. In case a stuck at HIGH is detected

the communication is rejected and the SPIE is set with the next communication.

SDO stuck at

The SDO stuck at GND and stuck at HIGH has to be detected by the SPI master. As the definition of the GSB

guarantees at least one toggle, a GSB with all -‘0’ or all -‘1’ reports a stuck at error.

L99DZ320

Serial peripheral interface (SPI)

DS14235 - Rev 5

page 89/146

L99DZ320 データシート(PDF) 89 Page - STMicroelectronics