L9908 datasheet(105/153 Pages) STMICROELECTRONICS

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5.20.1

Protocol description

L9908 implement a SPI-slave interface based on a 32-bit protocol.

This slave interface then always requires a SPI-master device (ex. uC) which is responsible to generate the

selection and the synchronization signals (NCS, SCLK) necessary to the data transmission.

The interface supports star mode connections along with other SPI-slave devices while it does not support

daisy-chain mode connections (input data aren`t transmitted directly to output port).

Figure 80. SPI connection modes "a" star connection (supported) "b" daisy-chain connection (not

supported)

The data exchange has an out-of-frame structure: each MISO output frame is related to the previously transmitted

MOSI frame.

SPI-master can directly verify if the previous frame has been received and processed correctly.

NCS pin (chip select) is used by the SPI-master to enable/disable the data communication. Communication starts

with the NCS falling edge while is stopped with the NCS rising edge. As long as NCS is high any transition at the

SCLK and SDI pins (including glitches) is ignored and SDO is forced into a high impedance state.

SCLK pin (Synchronous Serial Clock) is used by the SPI-master to synchronize the data communication. Each

correct communication shall contain 32 SCLK pulses.

At each SCLK rising edge SDI and SDO data are updated respectively by SPI-master and L9908 (shift), at each

SCLK falling edge SDI and SDO data are sampled respectively by L9908 and SPI-master (capture). SCLK has to

be low during NCS transition.

SDI pin (Serial Data Input) is used by the SPI-master to deliver the 32-bit input frame to L9908. In MOSI

communication the first bit expected is MSB while the last is LSB.

SDO pin (Serial Data Output) is used by L9908 to transmit the 32-bit data output. In MISO communication the first

bit transmitted is MSB while the last is LSB.

Figure 81. SPI timing diagram

Table 102. SPI timing characteristics

Symbol

Parameter

Test Condition

Min Typ Max Unit

SPI_fclk

Transfer Frequency

50% duty cycle(1)

10 10.2 MHz

L9908

Serial Peripheral Interface (SPI)

DS13546 - Rev 3

page 105/153

L9908 Datasheet(PDF) 105 Page - STMicroelectronics