L99LD02 datasheet(35/66 Pages) STMICROELECTRONICS

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DS12448 Rev 3

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L99LD02

Serial peripheral interface (ST SPI standard)

5.3.2

Device application registers

The Device Application Registers are all registers accessible using OpCode ‘00’, ‘01’ and

‘10’.

An access to an unused address will not lead to any error. Any data read from an unused

address is not defined.

5.4

Protocol failure detection

To realize a protocol which fulfills certain failsafe requirements, a basic set of failure

detection mechanisms is implemented.

5.4.1

Clock monitor

During communication (CSN low to high phase) a clock monitor counts the valid SCK clock

edges. If the SCK edges do not correlate with the SPI Data Length, an SPIE is reported with

the next command and the current communication is rejected.

By accessing the Device Information Registers (OpCode = ‘11’), the Clock Monitor is set to

a minimum of 16 SCK edges plus a multiple of 8 (e.g. 16, 24, 32).

Providing no SCK edge during a CSN low to high phase is not recognized as an SPIE.

5.4.2

SCK polarity (CPOL) check

To detect wrong polarity access on SCK, the internal clock monitor is used. Providing first a

negative edge on SCK during communication (CSN low to high phase) or a positive edge at

last will lead to an SPI Error being reported in the next communication and the current data

is rejected.

5.4.3

SCK phase (CPHA) check

To verify that the SCK phase of the SPI master is set correctly a special Device Information

read, the CPHA setting of the SPI master is wrong and a proper communication cannot be

guaranteed.

5.4.4

CSN timeout

By pulling CSN low, the SDO is set active and leaves the tri-state 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

the timer end is reached, the current communication is rejected and the SDO is set to tri-

state condition. This error is not reported in any specific status register.

5.4.5

Data stuck



SDI stuck at GND



As a command with all data bits set to ‘0’ and OpCode ‘00’ on address b’000000 cannot

be distinguished from an SDI stuck-at-GND error, this command is not allowed. In case

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