L99PD08 datasheet(24/41 Pages) STMICROELECTRONICS

24 / 41 page

SPI

L99PD08

24/41

Doc ID 15872 Rev 3

Figure 9.

SPI frame structure

6.2.1

Serial clock (SCK)

This input signal provides the timing of the serial interface. Data present at Serial Data Input

(SDI) is latched on the rising edge of Serial Clock (SCK). Data on Serial Data Out (SDO) is

shifted out at the falling edge of Serial Clock (SCK).

The writing to the selected data input register is only enabled if exactly one frame length is

transmitted within one communication frame (i.e. CSN low). If more or less clock pulses are

counted within one frame the complete frame will be ignored and a SPI frame error is

signaled in the Global Status register. This safety function is implemented to avoid an

unwanted activation of output stages by a wrong communication frame.

Note:

Due to this safety functionality a daisy chaining of SPI is not possible. Instead, a parallel

operation of the SPI bus by controlling the CSN signal of the connected ICs is

recommended.

CSN

SDO

SDI

Command Byte

(8 bit)

Global Status Byte

(8 bit)

Data

(8 bit)

MSB

LSB

Data

(previous content of register )

Write Operation

CSN

SDO

SDI

Command Byte

(8 bit)

Global Status Byte

(8 bit)

All 0

(8 bit)

MSB

LSB

Data

(8 bit)

Read Operation

MSB

LSB

MSB

LSB

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