33880 datasheet(15/25 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33880

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

MCU INTERFACE DESCRIPTION

In operation, the 33880 functions as an eight-output serial

switch serving as a microcontroller (MCU) bus expander and

buffer, with fault management and fault reporting features. In

doing so, the device directly relieves the MCU of the fault

management functions. This device directly interfaces to an

MCU using a Serial Peripheral Interface (SPI) for control and

diagnostic readout. Figure 21 and Figure 24, page 16,

illustrate the basic SPI configuration between an MCU and

one 33880.

Figure 21. SPI Interface with Microcontroller

All inputs are compatible with 5.0 V and 3.3 V CMOS logic

levels and incorporate positive logic. Whenever an input is

programmed to a logic low state (<0.8 V) the corresponding

output will be OFF. Conversely, whenever an input is

programmed to a logic high state (>2.2 V), the output being

controlled will be ON. Diagnostics are treated in a similar

manner. Outputs with a fault will feedback (via DO) to the

microcontroller as a logic [1] while normal operating outputs

will provide a logic [0].

Figure 22 illustrates the Daisy Chain configuration using

the 33880. Data from the MCU is clocked daisy chain through

each device while the Chip Select (CS) bit is commanded low

by the MCU. During each clock cycle output status from the

daisy chain, the 33880 is being transferred to the MCU via the

Master In Slave Out (MISO) line. On rising edge of CS data

stored in the input register is then transferred to the output

driver.

Figure 22. 33880 SPI System Daisy Chain

Multiple 33880 devices can be controlled in a parallel input

fashion using the SPI. Figure 23 illustrates 24 loads being

controlled by three dedicated parallel MCU ports used for

chip select.

Figure 23. Parallel Input SPI Control

Receive

Buffer

Parallel

Ports

Logic

33880

MC68HCxx

Microcontroller

SCLK

MISO

MOSI

Shift Register

MC68xx

MCU

with

SPI

Interface

8 Outputs

MISO

MOSI

Parallel Port

SCLK

33880

SCLK

Parallel

Ports

MOSI

MISO

SCLK

8 Outputs

MC68xx

Microcontroller

SPI

SCLK

8 Outputs

SCLK

8 Outputs

33880 Datasheet(PDF) 15 Page - Freescale Semiconductor, Inc

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