33811 datasheet(10/18 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33811

ELECTRICAL CHARACTERISTICS

MICROCONTROLLER PARAMETRICS

SPI - MCU INTERFACE DESCRIPTION

The 33811 device directly interfaces to a 3.3V or 5.0V

micro controller unit (MCU) using 16 bit Serial Peripheral

Interface (SPI) protocol. SPI serial clock frequencies up to

3.2MHz may be used when programming and reading output

status information (production tested at 3.2MHz). Figure 5

illustrates the serial peripheral interface (SPI) configuration

between an MCU and one 33811.

Command data is sent to the 33811 device through the SI

input pin. As data is being clocked into the SI pin, status

information is being clocked out of the device by the SO

output pin. The response data received by the MCU during

SPI communication depends on the previous SPI message

sent to the device. Next SO response data is listed at the

bottom of each command table.

SPI Integrity Check

Checking the integrity of the SPI communication with the

initial power-up of the VDD and RESET pins is

recommended. After initial system start-up or reset, the MCU

will write one 16-bit pattern to the 33811. The first 8 bits read

by the MCU will be the fault status (SO message 1) of the

outputs. The second 8 bits will be the same bit pattern sent

by the MCU. By the MCU receiving the same bit pattern it

sent, bus integrity is confirmed. The second 16-bit pattern the

MCU sends to the device is the a command word and will be

operated on by the device accordingly on rising edge of CS.

Important A SCLK pulse count strategy has been

implemented to ensure integrity of SPI communications. SPI

messages consisting of 16 SCLK pulses and multiples of

8 clock pulses thereafter will be acknowledged. SPI

messages consisting of other than 16 + multiples of 8 SCLK

pulses will be ignored by the device.

Figure 5. SPI Interface with Microprocessor

Two or more 33811 devices may be used in a module

system. Multiple ICs may be SPI-configured in parallel or

serial. Figures 6 shows the configurations. When using the

serial configuration, 32-clock cycles are required to transfer

data in/out of the ICs.

Figure 6. SPI Parallel Interface with Microprocessor

33811

Microcontroller

Receive

Buffer

Parallel

Ports

Fault Bits

16-Bit Shift Register

Shift Register

MOSI

MISO

SCLK

Parallel

Ports

Microcontroller

33811

SCLK

MISO

MOSI

Shift Register

33811 Datasheet(PDF) 10 Page - Freescale Semiconductor, Inc

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