33911 datasheet(32/45 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33911

FUNCTIONAL DEVICE OPERATIONS

LOGIC COMMANDS AND REGISTERS

33911 SPI INTERFACE AND CONFIGURATION

The serial peripheral interface creates the communication

link between a microcontroller (master) and the 33911.

The interface consists of four pins (see Figure 20):

• CS—Chip Select

•MOSI—Master-Out Slave-In

•MISO—Master-In Slave-Out

•SCLK—Serial Clock

A complete data transfer via the SPI consists of 1 byte.

The master sends 4 bits of address (A3:A0) + 4 bits of control

information (C3:C0) and the slave replies with 4 system

status bits (VMS,LINS,HSS,LSS) + 4 bits of status

information (S3:S0).

Figure 20. SPI Protocol

During the inactive phase of the CS (HIGH), the new data

transfer is prepared.

The falling edge of the CS indicates the start of a new data

transfer and puts the MISO in the low-impedance state and

latches the analog status data (Register read data).

With the rising edge of the SPI clock (SCLK), the data is

moved to MISO/MOSI pins. With the falling edge of the SPI

clock (SCLK), the data is sampled by the receiver.

The data transfer is only valid if exactly 8 sample clock

edges are present during the active (low) phase of CS.

The rising edge of the Chip Select (CS) indicates the end

of the transfer and latches the write data (MOSI) into the

state.

condition. Reset condition is the condition causing the bit to

be set to its reset value. The main reset conditions are:

- Power-On Reset (POR): level at which the logic is reset

and BATFAIL flag sets.

- Reset Mode

- Reset done by the RST pin (ext_reset)

MOSI

MISO

SCLK

VMS LINS HSS

LSS

Read Data Latch

Rising Edge of SCLK

Change MISO/MISO Output

Falling Edge of SCLK

Sample MISO/MISO Input

Write Data Latch

33911 Datasheet(PDF) 32 Page - Freescale Semiconductor, Inc

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