L9800 datasheet(43/55 Pages) STMICROELECTRONICS

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11.5

SPI protocol

The content of MOSI and MISO during SPI communication is shown in the Figure 34. MOSI line represents the

frame sent from the MCU and the MISO line is the answer provided by the device.

Figure 34. Relation between MOSI and MISO

frame A

frame B

(previous

response)

response to

frame A

frame C

response to

frame B

The SPI protocol provides the answer to a command frame only with the next transmission triggered by the MCU.

11.6

SPI frame structure

11.6.1

MOSI frame structure

Each MOSI frame has 16 bits with the following structure:

•

A command bit R/W, ‘1’ for write, ‘0’ for read

•

5 ADDRESS bits

•

8 DATA bits

•

A PARITY bit, odd parity

•

A FR_CNT frame counter bit

The frame count bit (FR_CNT) is toggled at each reception of the SPI data frame. For each frame, the

microcontroller has to toggle this bit into the serial IN coherently with the internal device frame counter. If the

device frame counter is not consistent with the one from the microcontroller, an SPI error is generated and the

frame is rejected. The same behavior is expected for serial OUT.

R/W[15]

ADDRESS[14:10]

DATA[9:2]

PAR[1]

FR_CNT[0]

11.6.2

MISO frame structure

Each MISO frame has 16 bits with the following structure:

•

An ERR error bit, ‘1’ if an error happened in the previous transmission, ‘0’ otherwise

•

5 ADDRESS bits, for address feedback function

•

8 DATA bits

•

A PARITY bit, odd parity

•

A FR_CNT frame counter bit

The frame count bit (FR_CNT) is toggled at each reception of the SPI data frame. For each frame the

microcontroller has to toggle this bit into the serial IN coherently with the internal device frame counter. If the

device frame counter is not consistent with the one from the microcontroller, an SPI error is generated and the

frame is rejected. The same behavior is expected for serial OUT.

ERR[15]

ADDRESS[14:10]

DATA[9:2]

PAR[1]

FR_CNT[0]

11.7

SPI registers

The register banks are composed of 8-bit registers.

L9800

Serial peripheral interface (SPI)

DS14041 - Rev 2

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