Analog Integrated Circuit Device Data

Freescale Semiconductor

9

33884

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 33884 is a monolithic integrated circuit designed to

interface between external electrical system switches and

low voltage microprocessors via a Serial Peripheral Interface

(SPI). The 33884 monitors the OPEN/CLOSED status of

multiple external switches used in a system. The 33884

features four programmable Switch-to-Ground or Battery

sense inputs, 6 Switch-to-Ground sense inputs, 2 Switch-to-

Battery sense inputs, programmable Wake up Timer,

programmable Interrupt Timer, and programmable wetting

current settings. All inputs are protected for ESD transients

when implemented with the appropriate ESD capacitor.

There are numerous applications for this device in aircraft,

aerospace, robotic, process & control, automotive, and

security systems. Potential applications exist where switch

status verification for safety, fault tolerant operation, or

process control function purposes are critical.

The 33884 has four modes of operation: Sleep, Normal,

Polling, and Polling + INT Timer.

The 33884 is designed to provide a robust interface

between system switch contacts and a microprocessor. Each

33884 input provides the switch contact with high levels of

wetting current during switch closure. After the input switch

has been closed for 20 ms, the wetting current is reduced,

hence reducing power dissipation in the IC. The response to

a SPI command will always return Switch Status, Master/

Slave, INT Flag, and Mode settings. The following section

describes the programming modes and features of the

33884.

MICROPROCESSOR INTERFACE

The M33884 directly interfaces to 3.3 or 5.0 V MCU. SPI

serial clock frequencies in excess of 5.0 MHz may be used for

programming and reading switch input status. Figure 4 shows

the configuration between an MCU and one 33884.

Figure 4. SPI Interface with Microprocessor

The 33884, though originally designed for automotive use,

is very useful in a variety of other applications, i.e., computer,

telecommunications, and industrial fields. It is parametrically

specified over an input battery/supply voltage of 9.0 to 16.0 V

but is designed to operate over a considerably wider range of

5.5 to 26.5 V.

Two or more 33884 devices may be used in a module

system when implemented in a parallel or serial

configuration. Figure 5 and Figure 6 show the parallel and

serial configurations respectively. When using the Serial

configuration, 32 clock cycles are required for a complete

transfer of data to the 33884.

MC68HCXX

Microcontroller

33884

MISO

MOSI

16 Bit Shift Register

16 Bit Shift Register

RST

SCLK

CS

INT

SO

SI

INT

To Logic

Receive

Buffer

Parallel

Ports