L99MH98 datasheet(51/147 Pages) STMICROELECTRONICS

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6.4.2

Read access scenario

When a read communication must be performed the following steps must be considered:

•

Frame n

–

SDI:

◦

Bit 23 = 0 (read command on the OpCode)

◦

Bit 22 = Not used

◦

Bits 21 to 16 = Address of the register to read

◦

Bits 15 to 1 = Data can be set to ‘0’

◦

Bit 0 = Parity bit

–

SDO:

◦

Bit 23 = 0 (no SPI error or RESET in the previous access)

◦

Bit 22 = GSBN bit (1 = No fault)

◦

Bits 21 to 16 = Address of the register selected in the previous frame (n-1)

◦

Bits 15 to 1 = Data value of the register selected in the previous frame (n-1)

◦

Bit 0 = Parity bit

•

Frame n+1

–

SDI:

◦

Bit 23 = 0 or 1 (read or write command on the OpCode)

◦

Bit 22 = Not used

◦

Bits 21 to 16 = Address of the register to read or write

◦

Bits 15 to 1 = Data to write into the chosen register

◦

Bit 0 = Parity bit

–

SDO:

◦

Bit 23 = 0 (no SPI error or RESET in the previous access)

◦

Bit 22 = GSBN bit (1 = No fault)

◦

Bits 21 to 16 = Address of the register selected in the previous frame (n)

◦

Bits 15 to 1 = Data value of the register selected in the previous frame (n)

◦

Bit 0 = Parity bit

Figure 34. Read access scenario

Frame n

0 = Read

Address of the register

to read reg1

Data can be set all 0 – not used during read

command on registers not clear on read

SPI Error or RESET

0 means:

No SPI error in previous access (frame n-1)

No reset before this access

GSBN

1 means no fault

Address reg0, selected by SDI

during previous frame (n-1)

Data value of reg0 (selected by SDI during

previous frame (n-1)) saved at frame n cs falling

Frame n+1

SPI Error or RESET

0 means:

No SPI error in previous access (frame n-1)

No reset before this access

GSBN

1 means no fault

Address reg1, selected by SDI

during previous frame (n)

Data value of reg1 (selected by SDI during previous

frame (n)) saved at frame n+1 cs falling

new command

Address reg2

Data to write into reg2

L99MH98

Serial peripheral interface (SPI)

DS14611 - Rev 3

page 51/147

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