L99MC6 datasheet(32/55 Pages) STMICROELECTRONICS

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Functional description of the SPI

L99MC6

32/32

Doc ID 16523 Rev 2

For Read operations, the <communication error> bit in the <Global Status Register> is set,

but the register to be read is still transferred to the DO pin. If the number of clock cycles is

smaller than the frame width, the data at DO is truncated. If the number of clock cycles is

larger than the frame width, the data at DO is filled with ‘0’ bits.

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.

Note:

If the frame width is greater than 16 bits, initial Read of <SPI-frame-ID> using a 16-bit

communication sets the <communication Error bit> of the <Global Status> register. A

subsequent correct length transaction is necessary to correct this bit.

8.3

Write operation

OC0, OC1: operating code (00 for ‘Write’ mode)

The Write operation starts with a command byte followed by 1 data byte.

For Write cycles the <Global Status> register is followed by the previous content of the

addressed register.

The RAM memory area consists of 8-bit registers. All unused RAM addresses are read as

‘0’.

Failures are indicated by activating the corresponding bit of the <Global Status> register.

Note:

The register definition for RAM address 00H is device specific.

A register value of all 0 causes a device reset (interpreted as ‘Data-in short to GND’).

8.4

Read operation

OC0, OC1: operating code (01 for ‘Read’ mode)

The Read operation starts with a command byte followed by 1 data byte. The content of the

data byte is ‘do not care’. The content of the addressed register is shifted out at SDO within

the same frame (‘in-frame response’).

The returned data byte represents the content of the register to be read.

Failures are indicated by activating the corresponding bit of the <Global Status> register.

Table 18.

Command byte for Write mode

MSB

LSB

Operating code

Address

Table 19.

Command byte for Read mode

MSB

LSB

Operating code

Address

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