Datasheet

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SLIS110A − APRIL 2003 − REVISED MAY 2005
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description of the functional terminals (continued)
oscillator input (XIN)
The XIN terminal is the input to the inverter used for the oscillator circuit. An external clock signal from the MCU,
crystal, or ceramic resonator is configured with resistors and capacitors. To bias the inverter, a resistor (1 MΩ
typ) is placed across XIN and XOUT.
This clock signal is prescaled to set the internal sampling frequency of the A/D converter.
oscillator output (XOUT)
The XOUT terminal is the output of the inverter used for the oscillator circuit.
data output (SDO)
The SDO output is the SPI data bus reporting information back to the microprocessor. This is a 3-state output
with the output set to high-impedance mode when CS
is pulled to V
DD
. The high-impedance state can also be
programmed by setting a bit in the prescale word which takes precedence over the CS
setting. The output is
disabled when the CS
terminal is pulled high (V
DD
).
data input (SDI)
The SDI terminal is the communication interface for data transfer between the master and slave components.
The SDI has an internal pullup to V
DD
; the data stream is in 8-bit word format.
serial clock (SCLK)
The SCLK output signal is used for synchronous communication of data. Typically, the output from the master
clock is low with the IC having an internal pullup resistor to V
DD
. The data is clocked to the internal shift register
on the falling clock edge.
test (TEST
)
The TEST
terminal, when pulled low, allows the IC to enter the test mode. During normal operation, this terminal
is left open or tied high (V
DD
). There is an internal pullup to V
DD
(default).
feedback output for amplifiers (CH1FB and CH2FB)
The CHXFB are amplifier outputs for the sensor signals. The gain of the respective amplifiers is set using the
CHXFB and CHX input terminals (see Figure 1).
input amplifiers (CH1P, CH1N, CH2P, and CH2N)
CH1P, CH1N, CH2P, and CH2N are the inputs for the two amplifiers which interface to the external knock
sensors.
The gain is set by external resistors R1 and R2. The inputs and outputs of the amplifier are rail-to-rail compatible
to the supply V
DD
.
An internal multiplexer selects the desired sensor signal to process programmable through the SPI.