33884 datasheet(12/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33884

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

POWER-UP

On initial power-up all 33884 registers are cleared and the

device enters the Sleep mode. To exit the Sleep mode, a

valid command word is required to be received from the

microprocessor.

SLEEP COMMAND

Sleep mode can be entered by a SPI Sleep command or

asserting the RST pin. In Sleep mode all inputs are Tri–State

and all internal active pull up and pull down currents are

disabled. Sleep mode reduces the current drain to a

quiescent current level of 10

µA and disables the IC. Sleep

mode provides lowest quiescent current for the IC. Exit from

sleep mode requires a valid SPI RUN, TRI–STATE, or

METALLIC command.

RUN COMMAND

The Run command places the IC in one of three operating

modes:

1. This is the normal operating mode of the 33884. In

Normal mode the status of the input switches are

latched on falling edge of CS and data is returned to

the MCU via SPI. All programmed combinations of

source and sink currents, used for sensing purposes,

are always active in this mode. While in the Normal

mode, an interrupt is generated and sent to the

microprocessor whenever an external switch changes

its OPEN or CLOSED state. Prior to a switch closing,

the 33884 sources 0.75 mA of sustain current. When

the voltage at the input crosses the comparator

threshold, 14 mA of current is allowed to flow. The 14

mA wetting current shuts off after a 20 ms timer

expires.

2. The Polling mode reads a switch status periodically,

interrupting the microprocessor only when an external

switch is sensed as being CLOSED. When the 33884

senses all external switches to be OPEN, the Polling

mode of operation continues. When a switch is sensed

CLOSED, an interrupt is sent to the microprocessor,

transferring it’s operational mode to the Normal mode.

The Polling mode provides a reduction in quiescent

current by turning OFF all source and sink currents

during sensed switch OFF periods. The Polling mode

allows reduction of quiescent current by disabling sink

and source currents during switch OFF periods.

3. The Polling + INT Timer mode of operation is similar to

the Polling mode above, except with the addition of an

interrupt being sent to the microprocessor if a switch is

sensed CLOSED, or upon the internal interrupt timer

timing out. An interrupt is always ultimately sent to the

microprocessor in this mode. The microprocessor can

be programmed to read, or ignore the reported switch

status while receiving the interrupt. If a switch is

sensed CLOSED, operation automatically reverts to

the Normal mode. If all switches are sensed OPEN,

and the wake up timer (INT Timer) times out, the 33884

continues to operate in the Polling + INT Timer mode.

The wake up timer duration may be set much longer

than the polling time.

The command also programs the SP1 to SP4 sense inputs

(switch-to-battery logic [1] or switch-to-ground logic[0]).

Please refer to Table 17.

TRI-STATE COMMAND

A Tri-State command places all switch inputs into Tri-State

position. All comparators on input are disabled in this mode.

The device will return logic [0] for the switch status.

SPI PROGRAMMING

The 33884 uses the SPI in full duplex synchronous slave

mode for communication with the microprocessor. The 33884

is programmed via a 16-bit word command from the MCU.

The word is sent to the device with the MSB first. The

command word sent to the 33884 sets the mode of operation

in the device. Returning data received from the 33884 is the

status of the sensed input switch on the falling edge of CS.

Sixteen clock periods are required for each transmission to

be valid. After the 16 clocks, CS is returned to the inactive

state (logic [1]), command words are no longer accepted into

SI, and the SO pin is Tri-Stated. The response to a SPI

command returns status based on previous command word.

This previous command could be a hardware reset as well as

any of the other commands discussed in this section.

33884 Datasheet(PDF) 12 Page - Freescale Semiconductor, Inc

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