33884 Datasheet, PDF (9/21 Pages) Freescale Semiconductor, Inc – Switch Monitor Interface

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.
MC68HCXX
Microcontroller
MOSI
16 Bit Shift Register
MISO
33884
SI
16 Bit Shift Register
SO
Receive
Buffer
Parallel
Ports
SCLK
RST
CS
INT
INT
To Logic
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.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33884
9