ELECTRICAL CHARACTERISTICS
MICROCONTROLLER PARAMETRICS
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.
33811
Microcontroller
MOSI
MISO
SI
Shift Register
16-Bit Shift Register
SO
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.
SCLK
Receive
Buffer
Fault Bits
CS
Parallel
Ports
Figure 5. SPI Interface with Microprocessor
SPI Integrity Check
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.
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.
Microcontroller
33811
MOSI
SI
Shift Register
MISO
SO
SCLK
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.
SCLK
CS
Parallel
Ports
33811
SI
SO
SCLK
CS
Figure 6. SPI Parallel Interface with Microprocessor
33811
Analog Integrated Circuit Device Data
Freescale Semiconductor
10
FREESCALE [ Freescale ]
