L99MH98 datasheet(47/147 Pages) STMICROELECTRONICS

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Figure 31. SPI connection

CSN

SCK

SDI

SDO

L99MH98

SPI

μC

6.2

Clock and data characteristics

The L99MH98 SPI can be driven by a microcontroller with its SPI peripheral.

Any communication frame starts with the falling edge of the CSN (communication start). CLK must be low.

The SDI data is then latched at all following rising CLK edges into the internal shift registers.

After communication start the SDO leaves 3-state mode and presents the MSB of the data shifted out to SDO. At

all following falling CLK edges data is shifted out through the internal shift registers to SDO.

The communication frame is finished with the rising edge of CSN. If a valid communication took place (for

example, correct number of CLK cycles, access to a valid address, no parity error), the requested operation

according to the operating code will be performed (write or clear operation).

The SPI signal description is shown in the Figure 32.

Figure 32. SPI signal description

CSi

SCLKi

SDIi

SDOi

MSB

MSB - 1

MSB - 2

don’t

care

don’t care

don’t

care

MSB

MSB - 1

MSB - 2

LSB + 1

LSB

don’t care

LSB

don’t care

t10

t14

tristate

t16

t15

LSB + 1

t11

t12

Communication

with other device

when

communication

with same device

t13

6.3

Communication protocol

6.3.1

SDI frame

The device data-in frame consists of 24 bits (OpCode (1 bit) + Reserved (1 bit) + Address (6 bits) + Data Byte 2 (8

bits) + Data Byte 1 (7 bits) + Parity bit (1 bit)):

•

OpCode = The first transmitted bit (MSB) contains the operation code, which represents the command/

instruction that will be performed

•

Reserved = Not used in the SDI frame (MSB-1)

•

Address = The following 6 bits (MSB-2 to MSB-7) represent the register address on which the command/

operation will be performed

•

Data Bytes = The subsequent 15 bits (MSB-8 to MSB-22) contain the payload to write

•

Parity bit = Last bit (MSB-23) contains the parity bit for the integrity check

L99MH98

Serial peripheral interface (SPI)

DS14611 - Rev 3

page 47/147

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